Originally Posted by ironfistx
Unclear a lot of the time.
A tap is really a second output from a shorter portion of the wind of a pickup, effectively giving you an option for full and a lower powered pickup in the same pickup. It can be used in humbuckers and single coils.
A split is using only one coil of a humbucker, which is theoretically (if not practically) identical to a single coil, allowing you to use your humbucker as both a humbucker and a single coil. It is only possible on humbuckers with four conductors (the start and end of each coil are available for wiring options).
Tap is however often used to describe what is really a split.