Impedance Control PCB is the characteristic impedance of a transmission line formed by PCB conductors. It is relevant when high-frequency signals propagate on the PCB transmission lines. PCB Impedance Control is important for signal integrity: it is the propagation of signals without distortion.
Impedance control is matching PCB trace dimensions and locations with the properties of the substrate material to make sure that the strength of a signal traveling along a trace is within a required range. So Controlled impedance in the fabrication and design of PCB is a complex and broad topic.