There are quite a number of sites which give definitions of printing, paper and typesetting terms. Here are a few.

How to Print

Fonts.com

Printing Industry Exchange

Castle Print (UK)

PMCA (UK)

Edinburgh — City of Print (UK)

Neenah Paper

PrintWiki

A Dictionary of the Art of Printing (1882-3)

Etherington & Roberts: Dictionary

Typography Deconstructed