one-night stand

Short definition from Wiktionary

Noun

1. 1
   An occasion when a performer or team of them (especially in vaudeville) expects to perform at a theater for a single evening.
2. 2
   A single sexual encounter between two individuals, where at least one of the partners has no immediate intention or expectation of establishing a longer-term sexual or romantic relationship.
3. 3
   Either of the two partners involved in such a single sexual encounter.