Time Invariant
A system is time invariant if for a given input signal x(t) into the system gives y(t) then also for a given input signal x(t-to), for to as a real number, the output is y(t-to).
Time Variant
A system is time variant if for an input x(t) the output is y(t) and for input x(t-to), for to a real number, then the output is not y(t-to).
