1. an event or occurrence, especially one of some importance
The concert was the biggest happening of the year.
O concerto foi o maior acontecimento do ano.
2. a spontaneous or improvised theatrical or musical performance
The artists organized a happening in the street.
Os artistas organizaram um happening na rua.
3. adjective: trendy, fashionable, or exciting (informal)
That's a happening nightclub downtown.
Esse é um clube noturno que está em alta downtown.