Hashed Time-Locked Collateral Contract.

Would define scripts that lock bitcoin as collateral for a loan made on another blockchain, returned when the loan is repaid.

It describes two scripts, small programs that decide who can spend coins. A borrower locks bitcoin for a set time while borrowing another currency elsewhere. If they repay, they get the bitcoin back. If not, it can be swapped to cover the loan, or split between borrower and lender in shares agreed at the start.