A Python Enhancement Proposal, or PEP, is a design document that provides information to the Python community or proposes changes to the language. Each PEP outlines a new feature, improvement, or guideline, and includes a rationale for the proposal, technical specifications, and potential impact on the language. PEPs are essential for the development of Python, as they facilitate discussion and consensus among developers. The most notable PEP is PEP 8, which provides style guidelines for writing Python code, promoting readability and consistency across projects.