Common Cards: Unusal shared cards dealt onto the table because the deck has run out of enough cards to deal to all players. CommunityCards are technically common cards, but the "common card" term is generally reserved for games which have no community cards.
This situation is probably most frequent in a full table of 7-stud, which deals seven cards to each player. After accounting for seven cards per player, four BurnCards, and dropping TheStub, the most players than can be dealt all the way to the river with a 52 card deck is six. If this is likely to happen, the dealer must deal the last street (or streets, if necessary) onto the board as common cards to be used by all players when making their hands.