The backing or steaming of clams on heated stones, between layers of seaweed; hence, a picnic party, gathered on such an occasion.

a cookout at the seashore where clams and fish and other foods are cooked--usually on heated stones covered with seaweed

seafood picnic, esp. beach party

ad lib session, every man for himself, a jam session not in the groov= e.

earlier used honorifically to mean jam session; later used to denote an improvised or arranged session which doesn't come off.

Clambake is a 1967 musical film starring Elvis Presley.