An annotation of a variable or a class attribute.

When annotating a variable or a class attribute, assignment is optional:

class C:
    field: 'annotation'

Variable annotations are usually used for type hints: for example this variable is expected to take int values:

count: int = 0

Variable annotation syntax is explained in section Annotated assignment statements.

See function annotation, PEP 484 and PEP 526, which describe this functionality. Also see Annotations Best Practices for best practices on working with annotations.