Tablature
A letter or number notation for keyboard and fretted instruments.
What it means
A tablature notates not the sound but the fingering. It tells the player which key to press, which string to stop at which fret, which hole to cover — the sounding pitch results from this but is not shown separately. Herein lies its advantage and its limitation: it is tailored to a particular instrument and its tuning and is not readily legible for another.
In the notation
The forms are varied. Keyboard tablatures of the German-speaking world use letters for the notes, with signs placed above them for duration. Lute tablatures work with a staff whose lines represent not pitches but strings; on it stand numbers or letters for the frets, and above these again the values. Italian, French, and German lute tablature differ considerably in their stock of signs and reading direction. Today's guitar tablature follows the same basic idea: six lines for six strings, digits for the frets.
Musical use
From the fifteenth to the seventeenth century, tablature was the usual notation for lute and keyboard music, and a large part of this repertoire survives exclusively this way. Numerous intabulations also survive in it, that is, transcriptions of polyphonic vocal settings for one instrument. For performance practice, tablatures are especially informative, because they fix position and fingering unambiguously where a transcription into staff notation leaves several possibilities open. What they show worse is the voice leading: which line goes where, the player must work out.
With the electric bass, four lines stand for four strings. Many modern guitar tablatures do not show the rhythm, which is why they are often combined with staff notation.
Performance practice
If you play from a tablature, clarify first the tuning of the instrument it was written for — without it, the fingering sounds right and the music wrong. Follow the voices deliberately, even if the notation does not show them; mark the main line for yourself in polyphonic settings. And use, with modern guitar tablature, the notated text in addition, if one is available: rhythm and voice leading are more legible there.