Impedance is the amount of resistance to the current flow in a circuit at a specific frequency.
A pure resistor is non reactive - it's resistance value does not depend on the frequency of the applied voltage.
However, reactive components like capacitors & inductors, change resistance values based on the frequency of the signal entering into them.
Capacitors have high impedance at low frequencies and low impedance at higher frequencies. Inductors have low impedance at low frequencies and higher impedance at higher frequencies.