Noun drop-off has 3 senses

• drop-off(n = noun.process) falling off, falloff, slack, slump - 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"
is a kind of declension, decline in quality, deterioration, worsening
Derived form verb drop off₅

• drop-off(n = noun.object) cliff, drop - a steep high face of rock; "he stood on a high cliff overlooking the town"; "a steep drop"
has particulars: crag, precipice
is a kind of formation, geological formation

• drop-off(n = noun.event) decrease, lessening - a change downward; "there was a decrease in his temperature as the fever subsided"; "there was a sharp drop-off in sales"
is a kind of alteration, change, modification
has particulars: shrinkage, shrinking, casualty, sinking, attrition, dwindling, dwindling away, waning
Derived form verb drop off₁