I guess the subject says it all.

I am reasonably familiar with body.def but I don't know anything about the other files.

Thanks.

There should be documentations hanging around the internet for the most common used defs like bodyconv, equip, body and so on.
Do you have some specific .def file in mind or rather what are you trying to do would help more by answering your question

A lot of it is just curiosity. I think I did have something specific at the time but I can't remember it now.

Also, I was just wondering, if by modifying, certain DEF files it might be possible to get some new or interesting effects in-game.

I'll try searching for tutorials or descriptions of the various DEF files.

Thanks Tomi.

For eg the implementation of the dress tab in fiddler I needed to parse some of the def files. So you could grep in the fiddler sources to find some definition.
* sounds.def
* body.def
* bodyconv.def
* equipconv.def
* gump.def

Thanks Turley. I will do that.