https://doi.org/10.1351/goldbook.S05994
  1. A reaction is termed stereospecific if starting materials differing only in their @C01249@ are converted into stereoisomeric products. According to this definition, a stereospecific process is necessarily @S05991@ but not all stereoselective processes are stereospecific. Stereospecificity may be total (100%) or partial. The term is also applied to situations where reaction can be performed with only one stereoisomer. For example, the exclusive formation of @C01092@-1,2-dibromocyclohexane upon bromination of cyclohexene is a stereospecific process, although the analogous reaction with (E)-cyclohexene has not been performed.
  2. The term has also been applied to describe a reaction of very high @S05991@, but this usage is unnecessary and is discouraged.
Sources:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1167 [Terms] [Paper]
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2219 [Terms] [Paper]