Hearts is a trick-taking card game where you are trying to lose. Every heart you take costs a point, the queen of spades costs thirteen, and the player with the fewest points when someone reaches 100 wins the game.
The twist that makes it great is shooting the moon: take *every* heart and the queen, and instead of 26 points, everyone else gets 26 and you get nothing. That single rule means a hand that's going badly can sometimes be turned into a triumph, and it keeps opponents from dumping points on you carelessly.
Taking all thirteen hearts and the queen of spades in a single hand. Instead of scoring 26 points, you score zero and every other player takes 26 — which can turn a lost game around in one hand.
Hearts must be 'broken' first — someone has to discard a heart on a trick of another suit before hearts can be led. It stops a player dumping points immediately on the opening trick.
Thirteen — half the total available in a hand, which is why avoiding it dominates the strategy.