BIP stands for Bitcoin Improvement Proposals.
It is a document that summarizes various proposals through discussions to make Bitcoin easier to use, increase its security, and develop it through stable transactions and usage.
Proposals are made by Bitcoin developers and other community participants.
The BIP approval process begins with the dissemination of the proposal through the Bitcoin Project mailing list, followed by multiple engineers discussing its appropriateness, and then it is approved by the Bitcoin Core maintainers as a draft version of the BIP.
The proposed documents are numbered sequentially, starting with number 1, and are published at “https://github.com/bitcoin/bips“.
For example, the BIP 101 document proposes to relax the block size limit for Bitcoin.
Where the size of one block is 1 Mbyte, it is proposed that this limit be increased to a maximum of 8 Mbytes in 2016, and then doubled approximately every two years thereafter.
According to the document, the proposal is to raise the limit to 64 Mbytes by 2022 and to 8 gigabytes by 2036 to speed up the approval of transactions and block generation.