The number of wires you can safely put into conduit without overheating is called the conduit fill. Conduit fill depends on the wire size and type and the conduit size and type. While there are hundreds of possible combinations, you're likely to use only a few -- 14-, 12-, or 10-gauge wire, in one of four or five types of conduit. Conduit fill charts describe the allowable fill for common types of conduit.
Liquidtight flexible metal conduit (LFMC) has a liquidtight, nonmetallic, sunlight-resistant jacket over an inner flexible metal core.
Type-A liquidtight flexible nonmetallic conduit (LFNC-A) has a smooth core, a reinforcing layer, and a cover.
Type-B liquidtight flexible nonmetallic conduit (LFNC-B) has a core with built-in reinforcement.
Electrical metallic tubing (EMT) is a thin-walled metal pipe.
Rigid nonmetallic conduit (RNC) is PVC conduit.
Electrical nonmetallic tubing (ENT) is flexible, corrugated PVC.