In SegWit, the witness holds signatures and related data outside the traditional transaction structure.
The witness is a segregated section carrying the unlocking data (e.g., signatures, public keys). It reduces malleability and changes how transaction weight is calculated.
"A P2WPKH input's witness stack contains the ECDSA signature and the public key, separate from the legacy scriptSig."
All terms and definitions may update as the Cryptionary improves.