drop off

fall or diminish

• “The number of students in this course dropped off after the first test”

change from a waking to a sleeping state

• “he always falls asleep during lectures”

retreat

get worse

• “My grades are slipping”

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”

a steep high face of rock

• “he stood on a high cliff overlooking the town”
• “a steep drop”

a change downward

• “there was a decrease in his temperature as the fever subsided”
• “there was a sharp drop-off in sales”