Re: in-phase, out-of-phase, series, parallel. What does it mean?
Just to clarify for the original poster (I was in the exact same position 10 years ago

):
Two coils can either be: Series or Parallel
AND
In Phase or Out of Phase.
Series, In Phase is how most normal humbuckers are wired. That powerful, slightly more mid and bass heavy tone.
Parallel, In Phase is how stock Strat coils are connected in position 2 and 4 of the switch. A little less bass and more treble.
You can make either out of phase. Series, Out of Phase is a nasally tone, think some of Brian May's lead sounds. Parallel, Out of Phase can be quite weak and trebly.
That leaves basically 4 different ways to connect 2 coils, right?
To complicate things

you can wire some coils in series (HB) then in parallel, etc.
A Les Paul style guitar in the middle position has two sets of coils in series (each individual pickup, 2 coils), wired together in parallel.
(Well, maybe I didn't clarify things as much as give you more to think about.

)