Best Efforts Mortgage Lock

A message sent by President Benjamin Harrison to Col. Mortgage "Mort" Lock, just before Lock attempted to prove his theory that a person could cross the Mississippi River by getting shot from a cannon. He didn't make it.

It's also a clause that comes up in the mortgage industry.

You own a mortgage originator. You have a mortgage you want to sell on the secondary market, meaning you are looking to find some other financial institution to take the loan off your hands. A "best efforts mortgage lock" means you have to try your best (make your "best effort") to attempt to sell the mortgage at the stated price. However, you aren't required by the contract to actually end up selling it. It's basically a promise to do your best, but if you can't get a deal done, there's no contractual penalty.