The Rational Unified Process® is a Software Engineering Process. It provides a disciplined approach to assigning tasks and responsibilities within a development organization. Its goal is to ensure the production of high-quality software that meets the needs of its end-users, within a predictable schedule and budget. RUP enhances team productivity, by providing every team member with easy access to a knowledge base with guidelines, templates and tool mentors for all critical development activities.
RUP's activities create and maintain models. Rather than focusing on the production of large amount of paper documents, the Unified Process emphasizes the development and maintenance of models—semantically rich representations of the software system under development.
RUP is a guide for how to effectively use the Unified Modeling Language (UML). The UML is a industry-standard language that allows us to clearly communicate requirements, architectures and designs.
The Rational Unified Process is a configurable process. Mind you, No single process is suitable for all software development. The Unified Process fits small development teams as well as large development organizations.