There are many types of wire and cable insulations. Some wire is meant for indoor use, some for outdoor use and even some meant for underground. If you buy the cable with outdoor insulation and you only need it for indoor use then you will be over paying. You want just enough protection without paying too much money.

PVC insulation is the most basic which you'll find on cheaper indoor wire and cable. Hook up wire has PVC insulation and it's mostly meant for appliances and other indoor applications. PVC can't go outdoors or in conduit because it doesn't have protection against any type of moisture or weather.

Electrical wire has PVC insulation with a nylon coating over it. The nylon repels rain and moisture so that it can't hit the insulation or the bare copper. So THHN wire can go outdoors and in conduit, but it can't go directly underground. Romex is a cable that's made from THHN wires but it still can't go outdoors or in conduit because of the ground wire in it. There's a bare copper ground wire without insulation in the cable, but the PVC jacket isn't strong enough outdoors to protect the ground wire.

If you need an electrical wire outdoors that can do anything then UFB cable is what you're looking for. It has a tough jacket to protect against anything that could happen outdoors. It's also known as an underground cable because it's suited for direct burial in the ground without conduit or tray. UFB cable is made similar to Romex wire because it still has the THHN wires and a ground wire.

Those were mostly the insulation types in the electrical wire field. I'll get into the portable cord field in a different article. That has to do with the rubber insulation types for power cable and SO cable. Most of them can handle the outdoors so there are other variations that need to be accounted for. Just remember that if you're paying for it then make sure you need it all.