SegWit, or Segregated Witness, is a protocol upgrade for the Bitcoin blockchain network. It was activated in August 2017 and aims to increase the block size limit on the Bitcoin blockchain.SegWit does this by separating witness data, which includes signatures, from transaction data, allowing more transactions to fit into each block. This improves the scalability of the network and reduces transaction fees. Additionally, it also provides a fix for a security vulnerability called transaction malleability.