A contract I’m reviewing contains, as appendix A, a definition section. But it’s not referred to as a definition section. Instead, the heading is “Glossary of Terms.”
Here’s how Wikipedia describes glossaries:
A glossary, also known as a vocabulary, or clavis, is an alphabetical list of terms in a particular domain of knowledge with the definitions for those terms. Traditionally, a glossary appears at the end of a book and includes terms within that book that are either newly introduced, uncommon, or specialized. While glossaries are most-commonly associated with non-fiction books, in some cases, fiction novels may come with a glossary for unfamiliar terms.
So a definition section in a contract could indeed be described as a glossary. But that doesn’t make it a good idea. For one thing, glossary is a bit hifalutin—you can’t count on everyone knowing what a glossary is.
But more to the point, just because something is a glossary doesn’t mean you have to call it a glossary. Instead, you give the reader the information they need. The heading usually given to definition sections is “Definitions.” That’s more informative than “Glossary of Terms.”
More broadly, use of “Glossary” as a heading reminds me of the tendency, in traditional drafting, to value terms of art over clarity, as exhibited in, for example, use of the verb attorn instead of the simpler consent. See MSCD 13.56.