Port-A-Potty is one of the common names by which outdoor portable toilets, of the sort usually found on construction sites, are referred to. Other names include Port-A-Pot, Port-A-John, Sani-Can, Porta-Potty, Handy-John, Big Apple Portable Toilet, and Port-O-Let. I'm sure there are hundreds of others...
The basic features of such a portable toilet include a plastic enclosure with door and roof, a plastic tank to collect waste, which has a hole and toilet seat on top, a strange blue ooze inside the tank, a plastic pipe leading up through the roof, and a toilet paper holder.
Optional features seem to include a urinal, and the "Poly-Wash Stand", which is a self-contained sink (with its own fresh water supply tank).
When a portable toilet is deployed on site, its tank is filled with about two or three inches of some odd blue stuff. As far as I can tell, this blue stuff is similar to that used in the trap on a waterless urinal, which is supposed to float on top of waste in the tank, preventing odors. Unfortunately, it doesn't work.
You may be curious as to the function of the little pipe leading up to the roof. I always figured it was used to vent odors from the tank, until a portable toilet spent a few months on duty in my front yard during construction. That allowed me the rare opportunity to witness the service procedure by which the waste tank is emptied. A large proboscis mounted on the truck is placed down the tube, and used to suck out the tank's contents. After the emptying is finished, more blue goo is pumped in.
A much neater variation on the portapotty, usually found at large outdoor festivals, takes the form of a trailer, with builtin fresh water and waste tanks, and air conditioning! These are equipped with real sinks, toilets and urinals, and are quite pleasant to use.