PMC stands for Precious Metal Clay. It consists of microscopic particles of a precious metal in an organic binder. (Usually the metal is silver but gold may also be used.) When fired with a torch or in a kiln, the organic binder burns away and the metal particles fuse together leaving a solid metal piece. Then the piece is usually placed in a special tumbler which polishes the surface. The metal may be further worked with burnishing, texture, bending, and patina.
The PMC I use, sell, and feature in my class produces a piece that assays to 99.9% pure silver. It is the real thing. PMC is easy to use and is becoming increasingly popular with jewlery makers.
For an in-depth treatment of the subject, refer to the online PMC User Guide (in PDF format).