Fool's mate

Fool's Mate is a very rare checkmate in chess that can happen in just two moves. It's the shortest possible checkmate and relies on your opponent making a critical mistake at the very beginning of the game. 
Here's how it happens (playing as Black):
1.White's first move: White makes a poor opening move, typically moving their f-pawn forward to f3 or f4.
2.Black's first move: You (as Black) move your e-pawn forward to e6 or e5. This opens up a diagonal for your queen.
3.White's second move: White makes another mistake, moving their g-pawn to g4. This exposes their King and creates a clear path for your queen.
4.Black's second move (the checkmate): You move your queen to h4, delivering checkmate. White cannot block, capture the queen, or move their King to safety. 
Why it's called Fool's Mate:
This checkmate is called Fool's Mate because it only happens if your opponent makes such a beginner's mistake that allows their King to be checkmated so quickly. Moving the f and g pawns early in the game weakens the King's defense, especially on the diagonal, and can be exploited by an opponent aware of this pattern. 
Important Notes:
Fool's Mate is extremely rare in actual games because it requires your opponent to make very weak opening moves.
Even though it's uncommon, understanding Fool's Mate highlights the importance of protecting your f-pawn and being mindful of king safety in the opening.
You can also achieve a similar checkmate as White, but it typically takes more moves (at least 3).