Frets
Raised ridges across the fingerboard of instruments such as the guitar, lute, and viol.
What it means
Frets are narrow raised ridges set across the fingerboard of plucked and some bowed instruments such as the guitar, lute, and viol. When a string is pressed down behind a fret, the vibrating length of the string is shortened precisely to that fret, fixing the pitch clearly, rather than varying continuously as on unfretted instruments.
Musical use
On the modern guitar, frets are narrow metal strips; historically, lutes often used gut cords tied around the neck, which could be shifted to suit unequal tunings more precisely. Fret spacing follows the mathematics of equal semitone division, so each fret sounds one semitone higher than the one before it.
Frets should be distinguished from the fingerboard markers found on some bowed instruments, which serve only as visual guides without actually dividing the string. Unfretted instruments such as the violin or cello instead require precise, ear-controlled finger placement.