Describes a stringed musical instrument which normally would have frets but is without them. Frets are the little bars, usually made of metal, that run perpendicular to the strings on the neck of the instrument.

The term almost always describes an electric bass. The doublebass, while certainly a fretless instrument, is a member of thie violin family and has no frets by its definition. The earliest banjos made in the 18th century had no frets. The fretless banjo is still produced today in limited numbers and is used in some traditional American music.

The fretless bass, or any fretless instrument, has a much different sound than its fretted counterpart. The sonic differences are mostly in the ADSR envelope: after the initial attack the note can grow slightly louder and more intense before beginning to get softer. The lack of frets gives the player much more control over the tone and timbre of the note being created, and the ability to generate vibrato is greatly enhanced. It gives the electric bass more of a bwwwwwaaaaaaa sound than its normal booooohhhhhmmmmmmm sort of sound.

If one is accustomed to playing a fretted instrument, it can be difficult to play a fretless instrument as there is no visual indication as to where one should press down to make a certain note. The player must stop the string at exactly the correct spot or the pitch of the note will be incorrect. Playing the notes with correct pitch is referred to as playing with proper intonation. Some instruments have fret lines where the frets should be (or where they used to be), and most instruments have dots on the side of the neck indicating where some of the frets would lie. Also, a normal vibrato technique on a fretted instrument bends the string back and forth, while one must use a violin vibrato technique, only applying motion parallel to the string.

The fretless electric bass was brought to fame by Jaco Pastorius. Some other fretless players of note include: Victor Wooten, Alain Caron, Les Claypool and Michael Manring, all terrifyingly skilled players and talented musicians.

Also describes a (less than prolific, but very kind-hearted) E2 noder.