Last year at AZ, Marcus and I co-hosted the
cel panel.  Basically at the panel we
went over what a cel was, how they are used in
a production, different types of cels, cel
terms used, etc.

A summary is at 
http://www.fansview.com/2000a/031100a.htm
Not everything in that summary was written
down correctly, but the errors in recording
don't effect getting general overview.