Definition from Wiktionary, the free dictionary
Alternative forms 
- (idiomatic, nautical) Something unlikely; something that has little chance of happening or working. The term arose from the accuracy of early ship guns, which were effective only at close range and unlikely to hit the mark at any great distance.
- We can try your plan, but it's a long shot and it probably won't work.
- (film) A master shot, the primary wide shot of a scene into which the closeups will be edited later.