A "handshake agreement" is a deal or agreement made between two people or parties that is sealed with a handshake. It means that both parties trust and agree on something without any formal written contract or legal documentation. Full definition
This contract between property owner and the cleaning professional improves upon the typical handshake agreement by clearly specifying schedule, fees and responsibilities in a legal document. (rocketlawyer.com)
But that doesn't mean that it's never possible — that in three or six months more time the legal jargon couldn't be pulled together — that the world would be doomed to a toothless, unenforceable handshake agreement - in - words - only that no nation would ever feel compelled to live up to. (treehugger.com)
A couple simply living apart is not legally separated regardless of the length of time, and they do not have the benefits of any court orders, so enforcing handshake agreements may be difficult. (divorcesource.com)