godan verb (-su)
burst into laughter; start laughing
Describes the sudden onset of laughter, often involuntary or triggered by something funny.
彼の冗談を聞いて、みんなが笑い出した。
Hearing his joke, everyone burst into laughter.
あまりにおかしくて、思わず笑
It was so funny that I couldn't help but start laughing.