Two definitions - a modification to an insurance policy or loan agreement to reflect new commercial or contractual terms. OR Signing the back of a cheque or Bill Of Exchange to transfer the ownership to someone else.
It is NOT:- an offence on a driving licence. It is NOT:- a film stars support for a product or advertisement. It IS:- Signing the back of a cheque to assign the value to someone else. It IS:- Formally modifying a contract.