A time-invariant (TIV) system is a system whose output does not depend explicitly on time. Such systems are regarded as a class of systems in the field of system analysis. Lack of time dependence is captured in the following mathematical property of such a system:
- If the input signal produces an output then any time shifted input, , results in a time-shifted output
This property can be satisfied if the transfer function of the system is not a function of time except expressed by the input and output.