the act of to women (lesbians or bi) having sex by bumping there vagina's against eachother.
dude, i caught my ex and my mom clam bumping last night
by juneaus November 06, 2004
The illusory idea that homosexual women may have sex by bumping one female's vaginal labia against another female's vaginal labia. A slander. Other forms: clam bumper(s).
"Those dikey chicks are off to go clam bumping."
by Spud January 27, 2004