Infinite impulse response (IIR) is a property applying to many
linear time-invariant systems. Common examples of linear time-invariant systems are most
electronic and
digital filters. Systems with this property are known as
IIR systems or
IIR filters, and are distinguished by having an
impulse response which does not become exactly zero past a certain point, but continues indefinitely. This is in contrast to a
finite impulse response in which the impulse response
h(
t)
does become exactly zero at times
t >
T for some finite
T, thus being of finite duration.