The set of descriptors (values of physicochemical, topological, geometrical, and electronic properties derived from the molecular structure) come mostly from ADAPT (the software system created by Professor Peter Jurs and coworkers at the Pennsylvania State University to study molecular structure - biological activity relationships SAR and molecular structure - physicochemical property relationships SPR) and MOPAC (general-purpose semiempirical molecular orbital package developed by Professor James Stewart).
For every descriptor an additional mathematical operation can be done on its value. Math functions can be applied in the Math functions page.
ADMEWORKS ModelBuilder includes 400 predefined descriptors (2D and 3D) and an unlimited number of substructure-related descriptors. Detailed list of all descriptors is available here