MIPS is the name of a company, processor core and instruction set.

MIPS processors are a simple RISC architecture and were best known for being the processor at the heart of many Silicon Graphics machines as well as being the processor on the original Sony Playstation.

MIPS the company now make almost all of their money designing processor cores and licensing them to other manafacturers who place this core inside their products.

The instruction set is very simple and easy to learn and was used for many years as a teaching architecture for the Computer Systems course at WaikatoUniversity before being replaced with a full custom design.

http://www.mips.com for lots more information and documentation