A fret is a raised portion on the neck of a stringed instrument, that extends generally across the full width of the neck. On most modern western instruments, frets are metal strips inserted into the fingerboard. On historical instruments and some non-European instruments, pieces of string tied around the neck serve as frets.
Frets divide the neck into fixed segments at intervals related to a musical framework. On instruments such as guitars, each fret represents one semitone in the standard western system where one octave is divided into twelve semitones.
"To fret" is often used as a verb, meaning simply "to press down the string behind a fret."
An advantage of frets is that they make it much easier to achieve an acceptable standard of intonation since the positions for the correct notes are given by the frets. Furthermore, playing chords are much easier on a fretted fingerboard.
A disadvantage of using frets is that the player is restricted by the temperament given by the position of the frets. Some influence on the intonation is still possible, however. The string can be pulled to the side to increase the string tension and the pitch. This technique (commonly called 'bending') is often used by electric guitarists of all genres and is a very important part of sitar playing. On instruments with thicker frets, the string tension and pitch will vary with the pressure of the finger behind the fret. Sometimes it is also possible to pull the string toward the bridge or nut, thus lowering or raising the string tension and pitch, respectively. However, with the exception of instruments like the sitar, where extensive pulling of the string is possible, much less influence on the intonation is possible than on unfretted instruments.
Since the intonation of most modern western fretted instruments is equal tempered, the ratio of the distances of two consecutive frets to the bridge is , or approximately 1.059463. Theoretically, the twelfth fret should divide the string in two exact halves. To compensate for the increase in string tension when the string is pressed against the frets, the bridge position can be adjusted slightly so that the 12th fret plays exactly in tune.
Many instruments' frets are not spaced according to the semitones of equal temperament, including the Appalachian dulcimer (with frets in a diatonic scale), the Turkish Saz (with frets spaced according to the Makam system of Turkish folk music), the Arabic Buzuq (with frets spaced according to the Arabic Maqam system), and the Persian setar and tar (with frets spaced according to the Persian Dastgah system), and the Turkish tanbur (with as many as 5 frets per semitone, to cover all of the commas of the Turkish Makam system).
Slanted frets: Most frets are perpendicular to the instrument's neck. Though slanted frets might be more ergonomic, few luthiers offer slanted or fanned frets; Rickenbacker offered them in the late 60's, and Novax Guitars offers such guitars today. The appearance of angled frets on these modern instruments belies the antiquity of this technique. Fanned frets first appeared on the 16th century Orpharion, a variant of the lute.
Scalloped fretboard: Scalloping involves the wood between some or all of the frets being scooped out. This allows a lighter touch for faster playing and also opens up new options for altering the pitch by bending the strings with the fretting hand. It had some popularity with musicians playing heavy metal music, although the concept can also be seen in more ancient instruments such as the sitar.
Retractable frets: In a retractable fret system, the frets on the fingerboard are designed to withdraw into the fingerboard and flush with the surface. This produces a smooth fingerboard surface like that of a fretless instrument, and allows the instrument to played as such. This lends versatility by allowing players to switch between fretted and fretless characteristics on the same instrument rather than forcing them to carry two separate instruments or a double-necked instrument. However, in practice, the current design requires the mechanism to be housed in the base of neck, occupying a significant amount of space just below the fingerboard surface. This prevent frets from being inserted into the top of the housing and reduces its musical range as a fretted instrument, although the housing may still be used as a fretless fingerboard surface.
It is also possible to find semi-fretted instruments; examples include the Malagasy kabosy and the Afghan Rubab. Semi-fretted versions of guitars and other fretted string instruments, however, are usually one-off, custom adaptations made for players who want to combine elements of both types of sound. One arrangement is for the frets to extend only part of the way along the neck so that the higher notes can be played with the smooth expression possible with a fretless fingerboard. Another approach is the use of frets that extend only partway across the fretboard so that some courses of strings are fretted and others fretless, for example Ryszard Latecki's Latar