From WordNet (r) 2.0 (August 2003) [wn]:
drop-off
n 1: a noticeable deterioration in performance or quality; "the
team went into a slump"; "a gradual slack in output"; "a
drop-off in attendance"; "a falloff in quality" [syn:
slump, slack, falloff, falling off]
2: a steep high face of rock; "he stood on a high cliff
overlooking the town"; "a steep drop" [syn: cliff,
drop]
3: a change downward; "there was a decrease in his temperature
as the fever subsided"; "there was a sharp drop-off in
sales" [syn: decrease, lessening] [ant: increase]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
drop-off \drop-off\ n.
1. a noticeable decline in performance; as, a drop-off in
attendance. [WordNet sense 1]
Syn: slump, falloff, falling off.
[WordNet 1.5]
2. a steep high face of rock.
Syn: cliff. [WordNet sense 2]
[WordNet 1.5]
3. a change downward; as, there was a sharp drop-off in
sales. [WordNet sense 3]
Syn: decrease, lessening.
[WordNet 1.5]