A guitar tablature, known as tab, is a diagram of strings where finger positions are indicated using numerals corresponding to the appropriate frets. Vertical lines represent the strings of an instrument and the horizontal lines represent the frets and dots indicate finger positions.

The series of horizontal lines forms what is called a staff or stave. Each line represents a string, and the standard acoustic guitar tab has a six-line staff. Numbers are written on the lines. Each represents a fret on the instrument. For example, a number 3 written on the top line means that the player should press down on the high E (top/thin) string (and not the low E, which is thicker) at the third fret. Number 0 stands for an open string.

To denote bends, hammer-ons and so forth, various lines, arrows and other symbols are used. A guitar tab is standardized, but different sheet music publishers adopt different styles in writing guitar music. Songbooks, guitar magazines and journals usually give a legend that specifies the style used.

The tab notation has several advantages over the standard musical notation, which uses a five-line staff. It is often easier and quicker for the player to interpret. Even those adept at reading the standard notation usually prefer the tab notation when it comes to learning to play guitar, because the acoustic guitar is a harmonic instrument, meaning that it plays multiple notes simultaneously. Moreover, acoustic guitar staff notation is written on a single staff compared with two for keyboard music. Therefore, it takes less time to read. The tab can also be easily represented using the ASCII code, which makes it easier to distribute electronically.

However, the tab is instrument specific, meaning that music written can only be played on guitar. Also, the tab only includes the pitch of the notes, and not rhythm. But rhythm can be indicated by notes or note stems written above the tab staff. This practice is sometimes adopted in guitar tab notation.