A Bitcoin Improvement Proposal (BIP) is a formal proposal for changing or upgrading the Bitcoin code. A BIP is implemented whenever the Bitcoin protocol undergoes large-scale changes that can significantly impact its blockchain and service.
Programmers can submit BIPs within the Bitcoin community, proposing changes to the software code of the Bitcoin network. The decentralized community then discusses and coordinates the proposals submitted, selecting the ones they agree on and implementing them to upgrade further and develop the Bitcoin protocol.
Any member of the Bitcoin community can submit a Bitcoin Improvement Proposal, which goes through careful review by miners, developers, and regular Bitcoin network users. Once a BIP gathers significant consensus from community members, the modified code is rolled out and awaits acceptance by the miners in the network.
Due to the sheer size and scale of the Bitcoin network, implementing a BIP successfully could take several years. A BIP needs to be approved by around 95% of miners before the community can upgrade the Bitcoin software version to incorporate the proposed changes.