PEP 484 is a Python Enhancement Proposal that introduced type hints to the Python programming language. It allows developers to specify the expected data types of function arguments and return values, enhancing code readability and maintainability. This feature helps catch errors early in the development process and improves collaboration among developers. The proposal was accepted in 2014 and became part of the Python 3.5 release. By using type hints, developers can leverage static type checkers like mypy to analyze code for type-related issues without executing it. This promotes better coding practices and helps ensure that code behaves as intended.