Recently I came across to the mesh library "vcg"(browse source , project page) developed by Visualization and Computer Graphics Lib in Italy. In one of the header file, I saw the term "wedge". Then I looked up in wikipedia and didn't find this term pertaining to computer graphics. After a short while googling, I found that this was originally described in the following paper.
Hugues Hoppe. Efficient implementation of progressive meshes. Computers and Graphics 22, 1 (1998), 27–36.
The main purpose of wedge is to allow represent discontinuities of material attributes on a mesh, as illustrated on the above image taken from the paper.