The act in which a man lies on his back as a girl sits reverse cowboy position on his face as he performs cunnilingus. The 'jellyfish' part comes in as the girl flails around as if she were a jellyfish when she climaxes. Usually done in orgies as it's not a physically tasking position for either participant, leaving both extra energy to continue in orgy activities.
John: 'Yo, me and dis bitch tried jellyfishing last night. It was the shit!'
Fred: 'Fuck yeah, I gotta get my girl to try that shit'
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