We assume people know what we know, don't we? But often others don't know what we know.
The South Central Regional Library Council realized that people didn't know the different terms used when talking about distance learning, so they created a Distance Learning Glossary. I'm sure there are more terms that could be added (like WebCT), but it is a long, wonderful list and useful to those who are unsure of the words they are hearing used. One might also use it to figure out alternate terms to use so that our language isn't so filled with jargon.
What terms do you use on your web site or in your institution that are not obvious to others? Should you also be creating a glossary for people to check?