The act of inserting both hands in a girls vagina
, interlocking the fingers, then while your hands are clasped, wiggling your fingers like an octopus.
If you want extra bang for your buck, you can keep your thumbs outside where they will be positioned perfectly to work on her clitoris
Bro 1: man that chick last night was fucked she kept telling me how her ex boyfriend would octofist her every time they fucked.
Bro 2: wow dude she must have had quite the octopussy