Classifiers
In UML visualization, a classifier is the superclass of classes, interfaces, and data types that have similar syntax and, therefore, are all notated by using a rectangle with keywords.
Because classes are most common in Unified Modeling Language (UML) diagrams, a rectangle without a keyword represents a class, and the other subclasses of classifiers are indicated with keywords.
Parent topic
About UML class diagrams
Related concepts
Class diagrams
Class shapes
Classes
Relationships
Attributes
Operations
Adornments for unresolved references
Multiplicity
Visibility