I would encourage you to maintain the “glossary of terms” separately from the BRD and reference it – with respect to the terms used to describe business items (as described above).

I would also add a glossary of definitions that defines esoteric, domain-specific, and project/company-specific terms. You can reference this from the BRD or include it within a BRD. If you have multiple BRD’s for a single client that can re-use the glossary, then make it separate and reference it. Otherwise, include it as a section within the BRD if that works better for you and your team.

Or did you mean something else?

I’m a big fan of clearly defining terms used in documents. It’s very easy for different people to talk about “the customer” or “the user” or “the server” or whatever and have different understandings. And it happens all the time. People can approach ideas or needs from different frames of reference (See http://onproductmanagement.wordpress.com/2007/07/29/frames-of-reference/), and at minimum, defining terms, roles, entities etc. clearly removes one area where confusion and possibly error can occur.