*Note:* Digital filters differ from continuous-time filters only in application. The parameters of digital filters are generally more stable than the parameters of commonly used analog (continuous) filters. Digital filters can be applied as optimal estimators. Digital filters are either finite impulse response (FIR) or infinite impulse response (IIR).

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

See also: Butterworth filter, Chebyshev filter