structural keys

https://doi.org/10.1351/goldbook.11519

A pre-established set of substructures the presence or absence of which are used to describe a molecule and are used during substructure searching as a filter to eliminate molecules that cannot match a query, for clustering or similarity searching, or for developing classification or regression models.

Example: ISIS keys are an example.
Source:
PAC, 2016, 88, 239. (Glossary of terms used in computational drug design, part II (IUPAC Recommendations 2015)) on page 257 [Terms] [Paper]