An altered seventh chord is a seventh chord with one, or all, of its factors raised or lowered by a semitone (altered), for example the augmented seventh chord (7+ or 7+5) featuring a raised fifth (C7+5: CEG♯B♭). Most likely the fifth, then the ninth, then the thirteenth.
In classical music, the raised fifth is more common than the lowered fifth, which in a dominant chord adds Phrygian flavor through the introduction of ♭. (for example, in C the dominant is G, its fifth is D, the second scale degree)
See also 
- ^ a b c Aldwell, Edward; Schachter, Carl; and Cadwallader, Allen (2010). Harmony & Voice Leading, p.601. ISBN 9780495189756.
- ^ a b Davis, Kenneth (2006). The Piano Professor Easy Piano Study, p.78. ISBN 9781430303343.
- ^ Christiansen, Mike (2004). Mel Bay's Complete Jazz Guitar Method, Volume 1, p.45. ISBN 9780786632633.