What is SegWit?
A 2017 soft fork that moved signature data into a separate witness structure, fixing transaction malleability and effectively raising capacity.
Witness data is discounted in the weight calculation, so SegWit transactions occupy fewer virtual bytes and cost less at the same fee rate. Addresses starting bc1 use it.
Fixing malleability — the ability to alter a transaction's identifier without invalidating it — was the prerequisite for Lightning.
Related terms
Virtual byte (vB)
The unit transaction size is measured in for fee purposes, equal to four weight units, introduced so SegWit…
Lightning & scalingLightning Network
A network of payment channels built on Bitcoin that settles small payments off-chain, using the base layer…
NetworkSoft fork
A rule change that tightens what is valid, so old nodes still accept new blocks.
Keys & custodyAddress
A string encoding the conditions under which an output can be spent. Bitcoin's equivalent of an account…
This definition is part of the Bitcoin Logical glossary. For the fuller explanation, start with Learn, or see the live numbers on The Bitcoin Signal.