9 adds minor seventh and a major ninth intervals to a triad (Bb, D in these examples):
7(b9) adds minor seventh and ninth intervals to a triad (Bb, Db):
Maj9 adds major seventh and ninth intervals to a triad (B, D):
7(#9) adds minor seventh and augmented ninth to a triad (Bb, D#/Eb):
add 9 or omit 7 adds a ninth to a triad:
See also: