The computer encoding of a possible chemical reaction between two explicit or Markush structures or substructures, often with a mapping between the atoms in the starting material and those in the product.
See also: SMIRKS
Source: PAC, 2016, 88, 239. 'Glossary of terms used in computational drug design, part II (IUPAC Recommendations 2015)' on page 259 (https://doi.org/10.1515/pac-2012-1204)