Your question is probably not specific enough. If we are talking about how a system (eg filter, amplifier etc) modifies a signal, we usually call it the frequency response, in which further comprises a magnitude and phase responses.
As for distortion, it is usually more dominant in high frequency signals. This is because the electronic properties of all conductors would be more pronounced. During RF design for example, you will even have to take into account the dimensions of your pcb tracks and wires, wire spacing etc as all these contribute to stray capacitances and inductances. You can even make capaciters and inducters out of wires!