1. Aa

• A represents:
  • the first point of a triangle
  • the digit "10" in hexadecimal and other positional numeral systems with a radix of 11 or greater
  • the unit ampere for electric current in physics
  • the area of a figure
  • the mass number of an element in chemistry
  • the Helmholtz free energy of a closed thermodynamic system of constant pressure and temperature
  • a vector potential, in electromagnetics it can refer to the magnetic vector potential
  • an Abelian group in abstract algebra
  • the Glaisher–Kinkelin constant
• [math]\displaystyle{ \mathbb{A} }[/math] represents the algebraic numbers or affine space in algebraic geometry
• a represents:
  • the first side of a triangle (opposite point A)
  • the scale factor of the expanding universe in cosmology
  • the acceleration in mechanics equations
  • the x-intercept of a line using the line equation
  • the unit are for area (100 m²)
  • the unit prefix atto (10⁻¹⁸)
  • the first term in a sequence or series

2. Bb

• B represents:
  • the digit "11" in hexadecimal and other positional numeral systems with a radix of 12 or greater
  • the second point of a triangle
  • a ball (also denoted by ℬ ([math]\displaystyle{ \mathcal{B} }[/math]) or [math]\displaystyle{ \mathbb{B} }[/math])
  • a basis of a vector space or of a filter (both also denoted by ℬ ([math]\displaystyle{ \mathcal{B} }[/math]))
  • in econometrics and time-series statistics it is often used for the backshift or lag operator, the formal parameter of the lag polynomial
  • the magnetic field, denoted [math]\displaystyle{ \textbf{B} }[/math] or [math]\displaystyle{ \vec{B} }[/math]
• B with various subscripts represents several variations of Brun's constant and Betti numbers; it can also be used to mean the Bernoulli numbers
• b represents:
  • the second side of a triangle (opposite point B)
  • The impact parameter in nuclear scattering
  • the y-intercept of a line using the line equation
  • usually with an index, sometimes with an arrow over it, a basis vector

3. Cc

• C represents:
  • the third point of a triangle
  • the digit "12" in hexadecimal and other positional numeral systems with a radix of 13 or greater
  • the unit coulomb of electrical charge
  • capacitance in electrical theory
  • with indices denotes the number of combinations, a binomial coefficient
  • together with a degree symbol (°) represents the Celsius measurement of temperature = °C
  • the circumference of a circle or other closed curve
  • the complement of a set (lowercase c and the symbol ∁ are also used)
• C represents:
  • an arbitrary category
• [math]\displaystyle{ \mathbb{C} }[/math] represents the set of complex numbers
• A vertically elongated C with an integer subscript n sometimes denotes the n-th coefficient of a formal power series.
• c represents:
  • the unit prefix centi (10⁻²)
  • the molar concentration in chemistry
• c represents:
  • the speed of light in a vacuum
  • the third side of a triangle (opposite corner C)
• Lower case Fraktur [math]\displaystyle{ \mathfrak{c} }[/math] denotes the cardinality of the set of real numbers (the "continuum"), or, equivalently, of the power set of natural numbers

4. Dd

• D represents
  • the digit "13" in hexadecimal and other positional numeral systems with a radix of 14 or greater
  • diffusion coefficient or diffusivity in dimensions of [length^2 / time]
  • the differential operator in Euler's calculus notation
• d represents
  • the differential operator
  • the unit day of time (86,400 s)
  • the difference in an arithmetic sequence
  • a metric operator/function
  • the diameter of a circle

5. Ee

• E represents:
  • the digit "14" in hexadecimal and other positional numeral systems with a radix of 15 or greater
  • an exponent in decimal numbers. For example, 1.2E3 is 1.2×10³ or 1200
  • the set of edges in a graph or matroid
  • the unit prefix exa (10¹⁸)
  • energy in physics
  • electric field denoted [math]\displaystyle{ \textbf{E} }[/math] or [math]\displaystyle{ \vec{E} }[/math]
  • electromotive force (denoted [math]\displaystyle{ \mathcal{E} }[/math] and measured in volts), refers to voltage.
  • an event (as in P(E), which reads "the probability P of event E occurring")
  • in statistics, the expected value of a random variable
• e represents:
  • Euler's number, a transcendental number equal to 2.71828182845... which is used as the base for natural logarithms
  • a vector of unit length, especially in the direction of one of the coordinates axes
  • the elementary charge in physics
  • an electron, usually denoted e⁻ to distinguish against a positron e⁺
  • the eccentricity of a conic section
  • the identity element in a group

6. Ff

• F represents
  • the digit "15" in hexadecimal and other positional numeral systems with a radix of 16 or greater
  • the unit farad of electrical capacity
  • the Helmholtz free energy of a closed thermodynamic system of constant pressure and temperature
  • together with a degree symbol (°) represents the Fahrenheit measurement of temperature = °F
• F represents
  • force in mechanics equations
  • _pF_q is a hypergeometric series
  • the probability distribution function in statistics
  • a Fibonacci number
  • an arbitrary functor
• f represents:
  • the unit prefix femto (10⁻¹⁵)
• f represents:
  • the generic designation of a function

7. Gg

• G represents
  • an arbitrary graph, as in: G(V,E)
  • an arbitrary group
  • the unit prefix giga (10⁹)
  • Newton's gravitational constant
  • the Einstein tensor
  • the Gibbs energy
  • the centroid of a triangle
  • Catalan's constant
• g represents:
  • the generic designation of a second function
  • the acceleration due to gravity on Earth
  • a unit of mass, the gramme

8. Hh

• H represents:
  • a Hilbert space
  • the unit henry of magnetic inductance
  • the homology and cohomology functor
  • the enthalpy
  • the (Shannon) entropy of information
  • the orthocenter of a triangle
  • a partial sum of the harmonic series
  • magnetic field, denoted [math]\displaystyle{ \boldsymbol{H} }[/math].
• H₀ represents Hubble's parameter as measures today (100 h km·s⁻¹·Mpc⁻¹ with h being the associated error)
• [math]\displaystyle{ \mathbb{H} }[/math] represents the quaternions (after William Rowan Hamilton)
• ℋ ([math]\displaystyle{ \mathcal{H} }[/math]) represents the Hamiltonian in Hamiltonian mechanics
• h represents:
  • the class number in algebraic number theory
  • a small increment in the argument of a function
  • the unit hour for time (3600 s)
  • the Planck constant (6.626 069(57)× 10⁻³⁴ J·s)
  • the unit prefix hecto (10²)
  • the generic designation of a third function
  • the altitude of a triangle

9. Ii

• I represents:
  • the closed unit interval, which contains all real numbers from 0 to 1, inclusive
  • the identity matrix
  • the Irradiance
  • the moment of inertia
  • Intensity in physics
  • the incenter of a triangle
• I represents:
  • the index of an indexed family
• i represents:
  • the imaginary unit, a complex number that is the square root of −1
  • a subscript to denote the ith term (that is, a general term or index) in a sequence or list
  • the index to the elements of a vector, written as a subscript after the vector name
  • the index to the rows of a matrix, written as the first subscript after the matrix name
  • an index of summation using the sigma notation
  • the unit vector in Cartesian coordinates going in the X-direction, usual bold i

10. Jj

• J represents:
  • the unit joule of energy
  • the current density in electromagnetism denoted [math]\displaystyle{ \boldsymbol{J} }[/math].
  • the Radiosity in thermal mechanics
• J represents:
  • the scheme of a diagram in category theory
• j represents:
  • the index to the columns of a matrix, written as the second subscript after the matrix name
  • in electrical engineering, the square root of −1, instead of i
  • in electrical engineering, the principal cube root of 1: [math]\displaystyle{ -\frac{1}{2}+\frac{1}{2}i \sqrt 3 }[/math]

11. Kk

• K represents:
  • the unit kelvin of temperature
  • the functors of K-theory
  • an unspecified (real) constant
  • a field in algebra
  • the area of a polygon
• k represents
  • the unit prefix kilo- (10³)
  • the Boltzmann constant, this is often represented as k_B to avoid confusion with
  • the Wavenumber of the wave equation
  • an integer, e.g. a dummy variable in summations, or an index of a matrix.
  • an unspecified (real) constant
  • the spring constant of Hooke's law
  • the spacetime Curvature from the Friedmann equations in cosmology

12. Ll

• L represents:
  • Length, used often in quantum mechanics as the size of an infinite square well
  • Angular momentum
  • the unit of volume the litre
  • the radiance
  • the space of all integrable real (or complex) functions
  • the space of linear maps, as in L(E,F) or L(E) = End(E)
  • the likelihood function
  • a formal language
  • the lag operator in statistics
  • a Lucas number
• l represents:
  • the unit of volume the litre
  • the length of a side of a rectangle or a rectangular prism (e.g. V = lwh; A = lw)
  • the last term of a sequence or series (e.g. S_n = n(a+l)/2)
• ℒ ([math]\displaystyle{ \mathcal{L} }[/math]) represents:
  • the Lagrangian (sometimes just L)
  • Exposure (in particle physics)

13. Mm

• M represents:
  • the unit of length the metre
  • a manifold
  • a metric space
  • a matroid
  • the unit prefix mega- (10⁶)
  • the Madelung constant for crystal structures held by ionic bonding
• m represents:
  • the number of rows in a matrix
  • the slope in a linear regression or in any line
  • the mass in mechanics equations
  • the unit metre of length
  • the unit prefix milli (10⁻³)
  • a median of a triangle

14. Nn

• N represents
  • the unit newton of force
  • the Neutron number
  • the Particle number in thermodynamics
  • The number of particles of a thermodynamical system
  • the nine-point center of a triangle
• N_A represents the Avogadro constant which is the number of entities in one mole (used mainly in the counting of molecules and atoms) and is 6.022 141 79(30) × 10,²³ mol ⁻¹
• [math]\displaystyle{ \mathbb{N} }[/math] represents the natural numbers
• n represents
  • the number of columns in a matrix
  • the "number of" in algebraic equations.
  • A neutron, often shown as ¹₀n
  • the Number density of particles in a Volume
  • the unit prefix nano (10⁻⁹)
  • the nth term of a sequence or series (e.g. t_n = a+(n-1)d)
  • the principal quantum number

15. Oo

• O represents
  • the order of asymptotic behavior of a function (upper bound); see Big O notation
  • [math]\displaystyle{ (0,0,\ldots,0) }[/math] — the origin of the coordinate system in Cartesian coordinates
  • the circumcenter of a triangle or other cyclic polygon, or more generally the center of a circle
• o represents
  • the order of asymptotic behavior of a function (strict upper bound); see Little o notation
  • the order of an element in a group

16. Pp

• P represents:
  • the pressure in physics equations
  • the unit prefix peta (10¹⁵)
  • probability in statistics and statistical mechanics
  • an arbitrary point in geometry
• [math]\displaystyle{ \mathbb{P} }[/math] represents
  • the prime numbers
  • projective space
  • a probability (as in P(E), which reads "the probability P of event E happening")
• p represents
  • the unit prefix pico (10⁻¹²)
  • a proton, often p⁺ or Template:Subsupp
  • the linear momentum in physics equations
  • the perimeter of a triangle or other polygon

17. Qq

• Q represents:
  • heat energy
• [math]\displaystyle{ \mathbb{Q} }[/math] represents the rational numbers
• q represents:
  • the deceleration parameter in cosmology
  • electric charge of a particle

18. Rr

• R represents:
  • the Ricci tensor
  • the circumradius of a cyclic polygon such as a triangle
  • an arbitrary relation
• [math]\displaystyle{ \mathbb{R} }[/math] represents the set of real numbers and various algebraic structures built upon the set of real numbers, such as [math]\displaystyle{ \mathbb{R}^n }[/math]
• r represents:
  • the radius of a circle or sphere
  • the inradius of a triangle or other tangential polygon
  • the ratio of a geometric series (e.g. ar^n-1)
  • the separation of two objects, for example in Coulomb's law

19. Ss

• S represents
  • a sum
  • the unit siemens of electric conductance
  • the unit sphere (with superscript denoting dimension)
  • the scattering matrix
  • entropy
• s represents:
  • an arclength
  • the displacement in mechanics equations
  • the unit second of time
  • a complex variable s = σ + i t in analytic number theory
  • the semiperimeter of a triangle or other polygon
• 𝒮 ([math]\displaystyle{ \mathcal{S} }[/math]) represents a system's action in physics

20. Tt

• T represents:
  • the top element of a lattice
  • a tree (a special kind of graph)
  • temperature in physics equations
  • the unit tesla of magnetic flux density
  • the unit prefix tera (10¹²)
  • the stress–energy tensor
  • tension in physics
  • an arbitrary monad
• t represents:
  • time in graphs, functions or equations
  • a term in a sequence or series (e.g. t_n = t_n−1+5)
  • the imaginary part of the complex variable s = σ + i t in analytic number theory
  • the sample statistic resulting from a Student's t-test

21. Uu

• U represents:
  • a U-set which is a set of uniqueness
  • a unitary operator
  • in thermodynamics, the internal energy of a system
  • a forgetful functor
• U(n) represents the unitary group of degree n
• ∪ represents the union operator

22. Vv

• V represents:
  • volume
  • the unit volt of voltage
  • the set of vertices in a graph
  • a vector space
• v represents the velocity in mechanics equations

23. Ww

• W represents:
  • the unit watt of power
  • work, both mechanical & thermodynamical
  • in thermodynamics, the number of possible quantum states in Boltzmann's entropy formula
• w represents:
  • the coordinate on the fourth axis in four-dimensional space.

24. Xx

• X represents
  • a random variable
  • a triangle center
• x represents
  • a realized value of a random variable
  • an unknown variable, most often (but not always) from the set of real numbers, while a complex unknown would rather be called z, and an integer by a letter like m from the middle of the alphabet.
  • the coordinate on the first or horizontal axis in a Cartesian coordinate system, or the viewport in a graph or window in computer graphics.

25. Yy

• Y represents:
  • the unit prefix yotta- (10²⁴)
• Y represents:
  • a second random variable
• y represents:
  • the unit prefix yocto- (10⁻²⁴)
• y represents:
  • a realized value of a second random variable
  • a second unknown variable
  • the coordinate on the second or vertical axis (backward axis in three dimensions) in a linear coordinate system, or in the viewport of a graph or window in computer graphics.

26. Zz

• Z represents:
  • the unit prefix zetta (10²¹)
  • the atomic number in chemistry and physics
  • a standardized normal random variable in probability theory and statistics
  • The partition function in statistical mechanics
  • in meteorology, the radar reflectivity factor
• [math]\displaystyle{ \mathbb{Z} }[/math] represents the integers
• z represents:
  • the unit prefix zepto (10⁻²¹)
  • the coordinate on the third or vertical axis in three dimensional space
  • the view depth in computer graphics, see also "z-buffering"
  • the argument of a complex function, or any other variable used to represent a complex value
  • in astronomy, wavelength redshift
  • a third unknown variable