In general, an augmented chord is any chord which contains an augmented interva. An augmented sixth chord, for instance, has an augmented sixth between the highest and lowest notes. More specifically, the augmented chord is the three-note chord consisting of a major third and augmented fifth above the - if the root is C, the augmented chord consists of the notes C, E and G sharp. It can also be thought of as two major thirds stacked on top of one another, and thus resembles a major chord with a raised fifth. This particular chord is also known as the augmented.
In twelve tone equal tempered tuning, an augmented chord has 4 semitones between the third and fifth, 4 between the root and third, and 8 between the root and fifth. It is represented by the integer notation 0,4,8.
The augmented chord is considered dissonant, or unstable, and lacks tonal center or drive. It symmetrically divides the octave and is ambiguous as to root because an augmented chord built from any note of an augmented chord produces that same chord. (Courtesy of Wikipedia)
Augmented Chords, whose symbols include "Aug.", "aug.", "+", and "(+5)", are constructed from the first, third, and sharped fifth scale notes. Augmented Chords are not used very frequently in popular music but are commonly found in jazz. Click below for the best in free Augmented Chord lessons available on the web.