According to Wiktionary:
(narratology) A situation in a film, television series, etc. in which a potential or future romantic couple meet for the first time in a way that is considered adorable, entertaining, or amusing.
According to Dictionary.com:
A situation or occasion when potential romantic partners meet for the first time in a charming or amusing way.
According to Urban Dictionary:
Scenario in which two individuals are brought together in some unlikely, zany, destined-to-fall-in-love-and-be-together-forever sort of way (the more unusual, the better).
The way the characters meet in "Serendipity" or "When Harry Met Sally" or at least half the romantic comedies out there.