An appoggiatura is a musical ornament that consists of a non-chord tone, typically approached by a leap and resolved by a step to a chord tone. It adds expressiveness and tension to a melody, often occurring on a strong beat. In classical music, appoggiaturas are commonly used in compositions by composers like Wolfgang Amadeus Mozart and Ludwig van Beethoven. They enhance the emotional impact of a piece, allowing performers to convey deeper feelings through their interpretation.