Consider the PCB signal as it travels along a track controlling impedance means that we control the performance or speed of that signal at a point along a track. Related to resistance, capacitance and conductance of the track in question. The impedance is also measured in Ohms, it is different than resistance which is a DC characteristic. Impedance is an AC characteristic, meaning that it is related to frequency.
Design guidelines for stackups and impedances
Download our PCB design guidelines for Stackups and Impedances to get your design right from start.