hap·pen·ing / ˈhap(ə)ning/ • n. 1. an event or occurrence: altogether it was an eerie happening. ∎ a noteworthy or exciting event: an all-star, superstar, megastar happening.2. a partly improvised or spontaneous piece of theatrical or other artistic performance, typically involving audience participation: a multimedia happening.• adj. inf. fashionable; trendy: nightclubs for the young are the happening thing.