Phases of a Unified Process

Inception: Develops use cases that will drive the next increment of progress. Should be the shortest phase.
Elaboration: Identifies known risk factors. Design a system architecture that addresses those risk factors. Validates that system architecture. May use the Unified Modeling Language (UML) to create use case diagrams, preliminary class diagrams, and package diagrams.
Construction: Implements the system architecture. Produces new executable architecture baseline. Normally the longest phase.
Transition: Delivers executable architecture baseline to users, who will report bugs and request features that serve as inputs to the Inception phase of the next iteration.