What is Guitar tab?

Guitar tab (short for tablature) is a special kind of musical notation specifically for the guitar. In guitar tablature, there are 6 lines representing the strings on the guitar. The first line is the highest sounding string on the guitar and the sixth line is the lowest sounding string. The lines have numbers on them which indicate which frets to hold down when playing a note. The numbers are read from left to right. Tab is best illustrated with an example.

e------------------------0-----------------------------------------
B------------------------0----------------------------------------
G-------------------0----1------------------------------------------
D---------3--------------1-----------------------------------------
A----3---------3---------2-----------------------------------------
E------------------------0-----------------------------------------

The above means play the 3rd fret on the the A string, then play the 3rd fret on the D string, then play the 3rd fret on the A string again, and then play the open G string, then play an E chord. There are typically no timings indicated in guitar tab. Instead guitarists deduce timing from familiarity with the music. Sometimes there is an implied timing indicated by the spacing in between 2 notes