The Rational Unified Process (RUP) is a popular iterative software development process created by the Rational Software Corporation, now a division of IBM. The RUP is an extensive refinement of the (generic) Unified Process.

The RUP is not a single concrete prescriptive process, but rather an adaptable process framework. It is intended to be tailored, in the sense that development organizations and software project teams will select the elements of the process that are appropriate for their needs.

The Rational Unified Process (RUP) is also a software process product, originally developed by Rational Software, and now available from IBM. The product includes a hyperlinked knowledge base with sample artifacts and detailed descriptions for many different types of activities. RUP is included in the IBM Rational Method Composer (RMC) product which allows customization of the process.

source and more information : http://en.wikipedia.org/wiki/Rational_Unified_Process