Bitcoin Improvement Proposal or BIP, is a technical design document providing information to the bitcoin community, or describing a new feature for bitcoin or its processes or environment which affect the Bitcoin protocol. New features, suggestions, and design changes to the protocol should be submitted as a BIP. The BIP author is responsible for building consensus within the community and documenting dissenting opinions.
Bitcoin Improvement Protocols. RFC-like documents modeled after PEPs (Python Enhancement Proposals) which discuss different aspects of the protocol and software. BIPs describe hard fork changes in the core protocol that require supermajority of the Bitcoin community (or, in some cases, only miners) to consent on any change and accept it is an organized manner.
Malone, J.A (2015). Glossary of Bitcoin Terms and Definitions. United States: Lulu Press, Inc