The Unified Modeling Language was originally developed at Rational Software but is now administered by the Object Management Group (see link). It is a modelling syntax aimed primarily at creating models of software-based systems, but can be used in a number of areas. It is:

	Syntax only - UML is just a language; it tells you what model elements and diagrams are available and the rules associated with them. It does not tell you what diagrams to create.
	Comprehensive - it can be used to model anything. It is designed to be user-extended to fill any modelling requirement.
	Language-independent - it doesn't matter what hi-level language is to be used in the code. Mapping into code is a matter for the case tool you use.