The standard grips this chord is usually shown with.
Ab is Ab, C and Eb, a major triad. The shape this page opens on is written 431114, lowest string first.
Note by note. Ab is the root, C is the major third and Eb is the fifth.

Also written Abmaj, AbM or Ab major. The same chord either way; which spelling you meet depends on who wrote the chart.
There are 6 common shapes for Ab on the guitar, and 45 derived voicings in the triad family.
One note away. Change a single note of Ab and you have Abm (with one note moved), Absus2 (with one note moved), Absus4 (with one note moved), Abmaj7 (with one note added), Abadd9 (with one note added) or Ab5 (with one note taken away).
In which keys. Every note of Ab belongs to C minor (the ♭VI), C# major (the V), Eb major (the IV), F minor (the ♭III), Ab major (the I) and Bb minor (the ♭VII).
The common shapes, written lowest string first: 431114, xx1114, 466544, xx6898, x-11-10-8-9-8, x-11-13-13-13-11.
Under the hand. None of the shapes for Ab uses an open string, so every one of them is movable; the lowest sits at the 1st fret. 4 of the 6 need a barre. Together they cover the neck from the 1st fret to the 13th.
Triad. Three notes across one string set. Ab has x311xx, xx111x, x3111x, xx654x, xxx544, xx6544, 4665xx, x6654x.
What kind of chord this is. Ab is a major chord — root, major third, fifth. major chords on every root, and what they are for.
The common shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.