A lady, often but not uniquely, of Catholic education who engages in the time honoured Girls' School pastime of clamjousting. It is the noble martial art of clam-to-clam combat, where one girl grinds her clam against her opponent's. (aka Tribadism)
The collective noun is 'TILT' (From the medieval tournaments consisting of a number of jousts.)
"A tilt of clamjousters"
See also: boxgrazer, dieseldyke, mingeeta, rugmuncher, WRAC.
"That dorm has seen so much clamjousting the matresses squelch with fannybatter"