An NPC is a non-player controlled character. 

Admin are the NPC's for:
-Quests, to give you some challenge in them
-Jobs, so they arne't TOO easy...

You may have one NPC but he/she/it can't have too much affect on the storyline.

NPC's are just people that follow you around for one reason or another. If you are a squadron leader then the squadron doens't count as an NPC, but they are only ever with you for missions that the faction sends you on.

For factions/companies 4 PCs must be in your employment before you have any NPC (humans or aliens.) characters awarded to you. 