An unusual jump or double jump bid showing a fit for partner’s suit, a few cards in the suit bid and shortage elsewhere.
In terms of concept, a fragment bid is very similar to a splinter, except that you are not bidding your shortest suit. Playing fragment bids, 1♠-2♦-2♠-4♣ suggests that responder has a main suit of diamonds, spade support and three or four clubs, hence a heart shortage.