A relatively rare type of chord in music. It consists of a root tone, the note a major third above it, and the note a major third above the second note. It is also the same as a major chord with the fifth raised a half-step. Notated by appending a "+" to the root tone (e.g., the C augmented chord would be represented as C+) or by other rarer ways (Caug, C+5).

The notes included in the augmented chord for each note:

NAME |    TONES
-----+------------
Cb   |Cb  Eb  G
C    |C   E   G#
C#   |C#  E#  Gx
Db   |Db  F   A
D    |D   F#  A#
D#   |D#  Fx  Ax
Eb   |Eb  G   B
E    |E   G#  B#
E#   |E#  Gx  Bx
Fb   |Fb  Ab  C
F    |F   A   C#
F#   |F#  A#  Cx
Gb   |Gb  Bb  D
G    |G   B   D#
G#   |G#  B#  Dx
Ab   |Ab  C   E
A    |A   C#  E#
A#   |A#  Cx  Ex
Bb   |Bb  D   F#
B    |B   D#  Fx
B#   |B#  Dx  G#*
(where b = flat, # = sharp, and x = double sharp.)

*The third tone of B#+ would technically be F triple-sharp, but (1) there's no way to notate it properly, and (2) you'll probably encounter it 99% of the time as simply C+.

Of course, any of these chords can be inverted, or spelled out in a different order. The root position of an augmented chord uses the first tone first, the first inversion uses the second tone first, and the second inversion uses the third tone first. For example, the root position of the C augmented chord can be spelled C-E-G#, the first inversion can be spelled E-G#-C, and the second inversion can be spelled G#-C-E. Notice, interestingly enough, that the first or second inversion of an augmented chord is also the root position of another augmented chord; e.g., the first inversion of C+ is enharmonically equivalent to the root position of E+.

Some chords created by adding tones to the augmented chord are the augmented seventh chord, augmented major seventh chord, augmented ninth chord, or augmented major ninth chord. Notice that variants of the augmented chord are notated not by putting a "+" right after the root tone, but by notating the related major chord and then appending a "+5" (meaning, the fifth is raised a half-step) or "aug". For example, C major seventh is notated CM7; therefore, C augmented major seventh is notated either CM7+5 or CM7aug.

cf. major chord, minor chord, diminished chord