"Spontaneous laughter" means laughing without planning or thinking about it. It's when you suddenly find something funny and laugh naturally, without someone trying to make you laugh. Full definition
«I'd be chatting normally, then suddenly catch someone's eye, and we would both burst into fits of spontaneous laughter. (politics.co.uk)
Mr Bugri Naabu in response said «I have given it to my party», a response that sparked spontaneous laughter among other dignitaries who were accompanying the former president. (ghanapoliticsonline.com)
This week the Latinos Out Loud crew chop it up about the Frida Kahlo Barbie Doll, Barbara Streisand's cloned dog, Amazon's Alexa totally eerie spontaneous laughter for no reason and so much more. (manhattantimesnews.com)