Terpenes constitute a class of natural products whose carbon skeletons are assembled from repeating five-carbon isoprene (2-methyl-1,3-butadiene) units, corresponding to the general hydrocarbon formula (C₅H₈)ₙ, in which *n* denotes the number of isoprene units incorporated ^[1][2]. The biosynthetic precursors of all terpene skeletons are the two isomeric five-carbon building blocks isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), which are generated through two compartmentalized routes: the cytosolic mevalonate (MVA) pathway, which begins with acetyl-CoA, and the plastid-localized 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway, which derives from pyruvate and glyceraldehyde-3-phosphate ^[3]. Condensation of IPP with DMAPP and subsequent chain extensions by prenyltransferases yield the prenyl diphosphate intermediates of defined chain length—geranyl diphosphate (GPP, C₁₀), farnesyl diphosphate (FPP, C₁₅), and geranylgeranyl diphosphate (GGPP, C₂₀)—that serve as the immediate substrates for terpene synthases ^[3]. Terpene synthases (TPS) catalyze the committed, scaffold-forming step: metal-dependent ionization of the allylic diphosphate bond generates a reactive carbocation that undergoes cyclization, hydride shifts, methyl migrations, and proton transfers to produce the hydrocarbon skeleton of the terpene. The term is defined structurally by the number of C₅ units: hemiterpenes (one unit, C₅), monoterpenes (two units, C₁₀), sesquiterpenes (three units, C₁₅), diterpenes (four units, C₂₀), sesterterpenes (five units, C₂₅), triterpenes (six units, C₃₀), and tetraterpenes (eight units, C₄₀) ^[1]. Within the taxonomy of biosynthesis and engineering of terpenoids, the term designates this structurally defined class of isoprenoid hydrocarbons together with the enzymatic logic of TPS-mediated skeletal diversification that generates the carbon frameworks upon which downstream oxidative and functionalizing enzymes act ^[4].