Transformation of the independent variable:

[imsanjoykb]

Shifting- the signal can be delayed ( x(t-T) ) or advanced ( x(t+T) ) by incrementing or decrementing the independent variable (time here).
The shape of the graph remains same only shifted on the time axis.

Scaling- the signal can be compressed ( x(at), a>1 ) or expanded ( x(t/a), a>1 or x(at), 1>a>0 ).
Here the shape/behaviour of the graph of the signal changes as the fundamental time period changes. In compression the time period decreases and in expansion the time period increases.

Reversal- also called folding as the graph is folded about the Y-axis or T if given x(T-t).