What is the difference between a humbucker and a single coil, and what kind of pup does a precision bass have?

The Fender precision bass pickup was the first commercial humbucking pickup; beating out Seth Lover's design for Gibson by a few years.  It is just built in a split-coil arrangement, rather than parallel coils.

A humbucker has two coils that are wired in opposite fashion (one coil has its north magnets pointing up, while the other has the south magnets pointing up).  This helps to cancel the electric "hum" that accompanies the signal, making them quieter.  In many cases, the two coils (with their two magnets) are more powerful and thus louder than a single coil pickup.  A single coil pickup is just that: one single coil.  The tones are quite different, and some companies (Fender among them) do make "noiseless" single coil pickups.
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