A siganl is said to be Time invariant if the time shift in the input signal results in an identical time shift in the output signal. This means that if y[n] is the output of a siganl when input of the system is x[n] , then y[$ n_0 $-n] is the output when the signal is x[$ n_o $- n].
Example of the time invariant system is x(t)= 25t here the function doesnot depend explicitly on t.
