PAF stands for Patent Applied For. The early Gibson humbuckers were released to market before the patent had been granted on their design.

I'm not familiar with the term 'split poles'. Some pickups have adjustable pole pieces which can be set to give more even loudness across the strings.

A humbucking pickup has two coils of wire in it, allowing different options for connecting them. This is sometimes referred to as a split coil setup.