The 11th Chord adds another tone to the 11th chord and, hence the name, this tone is 13 steps from the root. If you are playing the piano you could play this chord with seven tones, but on a guitar only six tones is possible of course. Therefore some tone will always be excluded which can vary depending on the chord shape.
None for the moment in this category
There are also major and minor 11th chords for guitar. The abbreviations for these are maj11 (e.g. Cmaj11) and m11 (e.g. Cm11). In this case, the short abbreviations 11 indicate that it's an expanded dominant chord.
Alternative chord shapes
Besides the chord illustrated above, there is like always other ways to form a specific chord. The 11th chord can also be played as a barre chord with this shape:
In this chord shape, the root is there you hold your index finger (the lowest note).
See also 13th chords.