Pickups are wound to specific resistances to produce a certain type of sound.
Resistance is a function of wire size and wire length.
Wire length is also referred to as number of windings. Most pickups for modern steels vary from approximately 16K Ohms to 23K Ohms. That is, a 16K Ohms pickup will favor a brighter sound while a 23K Ohms pickup will produce a more mellow sound. Generally, all things being basically equal, the greater the resistance, the more emphasis that is placed on the low's. The vast majority of steel players use DC resistance to discuss pickups.