I replied to your post in the Gear section, simply because I came across that one first. This section is dedicated to more in-depth discussion, so I can go into a little more detail here.

Impedance is a frequency-dependant characteristic. That's why PU specs quote something like "1.2 k Ohms @ 1 kHz".

The impedance of an inductor is calculated as:

Z = 2 x pi x f x L where

Z is the impedance, in Ohms.
pi is the ratio of a circle's circumference to its diameter.
f is the frequency, in Hertz (cycles per second), and
L is the inductance of the coil, in Henries

You might see this formula written as Z = wL. w is the angular velocity of the current or voltage waveform at a given frequency. It is calculated as 2.pi.f, so you can see it all comes to the same thing.

Resistance is calculated as:

R = E/I where

R is the resistance, in Ohms
E is the voltage (Electromotive force), and
I is the current, in Amperes

You can see that while the impedance of a coil will change in direct proportion with the frequency, its resistance will not.

The resistance and inductance of a coil are fixed values that are determined by its physical properties. Because the two appear in series, the impedance can never be less than the value of the resistance. At DC, the frequency is 0, so there is no impedance due to inductance, but the resistance is always there.

As the frequency increases, the impedance of the coil increases. It usually becomes much larger than the resistance, which remains the same as it was at DC.