one-night stand

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A sexual encounter that is limited to only one occasion.
• noun A person that one has such an encounter with.
• noun A performance by a traveling musical or dramatic performer or group in one place on one night only.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An occasion when a performer or team of them (especially in vaudeville) expects to perform at a theater for a single evening.
• noun idiomatic A single sexual encounter between two individuals, where at least one of the parties has no immediate intention or expectation of establishing a longer-term sexual or romantic relationship. As the phrase implies, the relationship lasts for only one night.
• noun idiomatic A person with whom one shares a single sexual encounter.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a brief sexual encounter lasting only for a single night
• noun a performance in one place on one night only