What Is Tab? (or tablature)

From meem@gnu.ai.mit.edu

Tab is short for tablature (or tabulature, depending on which dictionary you're using). It's a different way of reading music than you may be used to: instead of each bar representing a certain note, they each represent a string. They are arranged so that the high E is represented by the top line and low E is represented by the lowest bar. If the strings use an unconventional tuning, the tuning will usually be shown next to the lines so you can see how each string should be tuned.

Unlike conventional written music, time values are very rarely shown in the tab. Instead, an estimate of how long it is between every plucked note (which is represented by the distance between the numbers in the tab) is commonly shown to roughly indicate timing.

Instead of representing the time of each note on the staff, a number representing the fret on that string is shown. So, for example:

e-------------------     ---0---------------     
B---13--------------     ---1-----2---------     
G---13--------------     ---0-------4-------     
D-------------------     ---2------------2--     
A-------------------     ---3---------------     
E-------------------     ---0---------------     

Play the 13th fret       Play a C chord, then wait,
on the second and        play the 2nd fret on the B
third strings at the     string quickly followed by
same time                the 4th fret on the G
                         string, then wait and play
                         the 2nd on the D string.

There are many other guitar techniques we all know and love. Usually these are explained by the author of the tablature, but here are some common ones:

----7/9-------  ----7^9r7------  ----7h9p7------- 

Slide from 7th  Bend from the    From the 7th fret,
to 9th fret.    7th up to a 9,   hammer onto the
                then release     9th, then pull off
                back to the 7th  to the 7th.

Of course there are tons of other techniques like tapping and pick sliding and whammy bar stuff, but all of that has not been standardized across all compu-tab, magazines, and books (yet).