Trebuchet
The trebuchet is a mutual zugzwang in which two kings stand on either side of a pair of locked pawns, each beside the enemy pawn, so whoever must move loses a pawn and the game.
Picture two pawns locked head to head on the d-file, White's on d4 and Black's on d5. A white king on e5 and a black king on c4 each stand next to the pawn of the other side, yet neither can capture it, because each pawn is guarded by its own king and the capture square touches the enemy king. Whoever has to move must step away, the other king takes a pawn, and the pawn ending is easily won. That is the trebuchet: a mutual zugzwang in which the player to move loses and the player who can wait wins.
The practical lesson is about timing. If you can reach the pattern with your opponent on move, you win; with yourself on move, you lose. So before committing, count the spare tempi each side has elsewhere, and look for a way to hand the move over, perhaps by a reserve tempo or a triangulation.
The typical mistake is walking into the formation without checking whose turn it will be, or leaving the guard of the pawn too early. Remember that a king beside its own pawn is only safe while the enemy king stays out of reach.
If "Trebuchet" has cost you half a point, a first lesson is a good place to find the pattern behind it: George Li goes through your games and builds a plan.
Related terms
A mutual zugzwang is a position in which whichever player has to move is worse off, so each side would gladly pass, and the result depends entirely on whose turn it is.
Zugzwang is the bind of having to move when standing still would be best: the player on move has only moves that weaken the position, and since passing is not allowed, the duty to move itself costs something.
Opposition is a standoff between the two kings on one file or rank with a single empty square between them; whoever does not have to move holds it, because the other king must give up ground.
A reserve tempo is a spare, harmless move, usually a pawn move, that one side can make without damaging its position, passing the obligation to move across to the opponent.
Triangulation is a way for a king to hand the move to the opponent: it makes a three-move loop over neighboring squares and returns to its starting square, while the enemy king, with less room, cannot copy the loop.
A king and pawn endgame is an ending in which only kings and pawns remain, so the result depends on promotion races, king placement, opposition, and exact counting of moves.
Guides that go further
What to decide first, the questions to ask, what a first lesson should show and the red flags to avoid.
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A game review, a read on your level and a written study plan from George Li.
Want to spot this in your own games?
A first lesson starts with your games: George reviews them and builds a study plan around what he finds.