drop-off

1. a change downward

    e.g. there was a decrease in his temperature as the fever subsided
           there was a sharp drop-off in sales

    Synonym: decrease lessening

2. a steep high face of rock

    e.g. he stood on a high cliff overlooking the town
           a steep drop

    Synonym: cliff drop

3. a noticeable deterioration in performance or quality

    e.g. the team went into a slump
           a gradual slack in output
           a drop-off in attendance
           a falloff in quality

    Synonym: slump slack falloff falling off