A Class is drawn as a solid-outline rectangle with three compartments separated by horizontal lines. The top name compartment holds the Class name and other general properties of the Class (including stereotype); the middle list compartment holds a list of properties; the bottom list compartment holds a list of operations. The property and operation compartments are optional and you can suppress them.

A Class is the descriptor for a set of objects with similar structure, behavior, and relationships. The model is concerned with describing the intention of the class, that is, the rules that define it. The run-time execution provides its extension, that is, its instances. 

Classes are declared in the Class diagrams and used in most of other diagrams. UML provides a graphical notation for declaring and using these Classes as well as a textual notation for referencing Classes within the descriptions of other model elements.

A Class represents a concept within the system being modeled. It has a data structure, Behavior, and relationships to other elements. The name of a Class has a scope within the package in which it is declared and the name must be unique (among Class names) within its Package.