BIP is an abbreviation for "Bitcoin Improvement Proposals." It is a public collection of documents created to discuss technical aspects of Bitcoin. It includes the specifications for the standard features already included in Bitcoin.
BIP100 is a proposed relaxation of the upper limit for a Bitcoin block size. It starts with the current block size maximum, 1 MB, and changes in the block size are decided every three months based on a vote by the miners up to a maximum of 32 MB.
BIP101 is a proposed relaxation of the upper limit for a Bitcoin block size. It sets the block size maximum at 8 MB in November 2016 and doubles the size about once every two years. In this proposal, it will be 64 MB in 2022, and by 2036 the maximum block size will be raised to 8 GB.