probably refering mostly to RGC
A "chase nipple" would look like a romex connector except the clamp part would be an oversized smooth edged flange(only need one locknut)
A "close nipple" would be the shortest piece of conduit you could thread (or buy) without having running threads the entire length.
A "short nipple" would constitute anything else. ie: normally sold as 3", 3 1/2", 4", 4 1/2" etc.
I have never heard the term used in connection with an elbow, but believing heat dissapation is the subject,why not. (?)
