1. American football A long forward pass with a low success of being caught, typically thrown in desperation at the end of a half. And he throws a Hail Mary! Ah, it's incomplete. No overtime tonight, folks. A: "I heard the quarterback threw a Hail Mary?" B: "Yeah, but that butterfingers receiver couldn't corral it." Smith threw a Hail Mary as time was expiring and just narrowly missed his tight end.

2. By extension, a final, usually drastic or risky effort to avoid failure or defeat that has a low probability of success, typically done in desperation. The experimental new medication will be something of a Hail Mary as doctors scramble to save the patient's life. The political candidate decried his opponent's new attack campaign as nothing more than a cheap Hail Mary attempting to distract the public at the last minute. Don't cram the night before the exam—that's nothing but a Hail Mary.