Jeff, it stands for polyethelene insulated conductors. Most outside plant cable uses this type of insulation and outer jacket, mainly because it's lighter and cheaper. It's terribly flammable though, so it can't be used indoors.
Prior to this, outside plant cables had conductor insulation made from paper, referred to as "pulp". This paper was waxed and formed tight and uniform binders within the cable to permit small diameter cables in congested vaults and manholes. The pairs weren't individual colors; they were all red-white, white-green, etc. on a per-binder basis. It's still available today, but not with the original outer sheath made of lead.
To protect the paper insulation from obvious destruction in the event water enters the cable, this type of cable is pressurized with nitrogen. Pressure sensors are placed at various points along the cable route to monitor this pressure. In the event of a pressure drop, an alarm is sounded in the central office for immediate repair.
As for all of those other questions, I don't have a clue. I am not old enough, although I already answered the spare pair question in another category yesterday
