ANSI Common Lisp 1 Introduction
1.7 Language Subsets
The language described in this standard contains no subsets, though subsets are not forbidden.
For a language to be considered a subset, it must have the property that any valid program in that language has equivalent semantics and will run directly (with no extralingual pre-processing, and no special compatibility packages) in any conforming implementation of the full language.
A language that conforms to this requirement shall be described as being a "subset of Common Lisp as specified by ANSI <<standard number>>."