Define Shifting and Reversing – Linear System?

The signal x[n - m] is said to be time-shifted by m samples, where m is an integer. If m is positive, the shift is to the right (delay in time) and when m is negative, the shift is to the left (advance in time). Examples of shifting in time are given below.

The signal x[-n] is said to be time-reversed (flipped about n = 0). This is shown in the example below.

The operations of time shifting and reversing can be performed in either order but some care must be taken.