UML(Unified Modeling Language) is a modeling language which helps to simplify the process of software design. UML includes a flexible graphical notification to create visual models of basically object-oriented software systems.
The UML was created by Grady Booch, Ivar Jacobson and James Rumbaugh of the Object Management Group.
Each symbol in the UML notation has well-defined semantics. UML is independent of any specific programming language and thus once a model written in the UML, it can be interpreted by any developer or any UML interpreting tool unambiguously.
Various diagrams in UML: