In telecommunication, fall time (pulse decay time) is the time required for the amplitude of a pulse to decrease (fall) from a specified value (usually 90 percent of the peak value exclusive of overshoot or undershoot) to another specified value (usually 10 percent of the peak value exclusive of overshoot or undershoot).

Limits on undershoot and oscillation (i.e. hunting) may need to be specified when specifying fall time limits.

Source: from Federal Standard 1037C and from MIL-STD-188