What are frets on a guitar and how do they affect the sound and playability of the instrument?

Frets are metal strips on the neck of a guitar that divide the fingerboard into different notes. They help players find the correct pitch for each note and enable them to play chords and melodies accurately. The placement of the frets determines the pitch of the notes produced when a string is pressed down. The closer a string is pressed to a fret, the higher the pitch. Frets also affect the playability of the guitar by providing reference points for finger placement and allowing for precise intonation.