How Do Segregated Witness (SegWit) and Block Weight Optimize Block Space?
SegWit is an upgrade that 'segregates' or separates signature data (witness data) from the transaction data. By moving witness data to a separate structure, it reduces the effective size of a transaction.
Block weight is a new metric introduced with SegWit, allowing blocks to be up to 4MB in weight, even though the base block size remains 1MB. This increases the transaction capacity without a full hard fork.