Bitcoin Improvement Proposal 174 concerns Partially Signed Bitcoin Transactions (PSBT).
BIP 174 proposes a format for partially signed bitcoin transactions. It is designed to be standardized and extensible, allowing different wallet implementations to pass messages around to collaboratively build transactions in a trustless manner. It also works well in situations of offline signing.
See: https://github.com/bitcoin/bips/blob/master/bip-0174.mediawiki
