What is meant by linear wave shaping?

If we give a input signal(it may be in form of sinusoidal or square or ramp or etc..)  to a low pass circuit we will get some distortion in output signal this is called as linear wave shaping.

Low pass circuit: A low pass circuit is that  which gives output signal only at low frequencies i.e even if we give input at high and mid band frequencies we will not get output