In playing video games I've decided that NPC isn't precise enough to describe all characters. In Dungeons and Dragons, where it started, it basically referred to everyone and everything that weren't PCs. I've seen it come to mean only other people, not monsters, but video games have added certain types of characters that didn't really exist in PnP games.

When your solo character gets a new companion, someone who joins your party, what do you call them? NPC? PC?
That doesnt seem right to me. I feel different terms are needed, so I've come up with this:

JPC (Joinable Player Character)
These are characters that are part of your party, that you fully control, but that you, the player, didn't create. They may have their own agendas and at certain parts of the game may do things out of your control, even leave. Aside from that though, they are nearly identical to the character you created in terms of gameplay. You equip them, control them, level them, make all decisions for them, etc. Jaheira and Khalid from Baldur's Gate, Carth and HK from KOTOR 1... these are examples of JPCs.

APC (Allied Player Characters)
These are between JPCs and NPCs. You don't get to look at their "sheet". You can't see their stats, their skills, their gear... you can't change anything about them, nor will you presumably control them for long. However, they are allied to you and you can control where they move, who they attack, and possibly what kind of attack they make. In Mount and Blade for example you can help villagers fight off raiding bandits. For the duration of the battle you can direct the villagers, even though you have no authority over them, can't see their specs, and they won't do anything you say outside the battle. They're not part of your party but you do have some control over them... making them more than standard NPCs.

It may be there are already terms out there for these types of characters... I don't watch streams or play online, and I don't really talk with fellow gamers. So if they already exist I'd love to hear them. But since I haven't, I came up with these. Maybe one you has similar terms, even better terms... feel free to share.

That's all. I was watching a let's play and disliked the LPer constantly referring to his party members as NPCs, so I felt compelled to write this. Like or dislike as you will.

They are called non playable characters for a reason, no need to make it more complicated then it have to be and invent a new word for them. Dislike the term as you may but it has been that way for a long time and people has gotten used to it.

Here's an example of a case that defies your classification: Dragon Quest 4.

In Chapters 1-4, you have two types of party members, those you can control directly, and those you can't (called UCs, or Uncontrollable Characters, in the English NES manual). You can view the character "sheet" for UCs, though they lack some of the stats your regular characters have, lack an inventory (though they have equipment if they're not a monster), can't cast spells outside of battle (except in remakes), and can't level up.

In Chapter 5, however, things get more complicated. The only character you can control directly (in the FC/NES version, anyway) is the hero/heroine; everyone else (except UCs, when they show up, which is only part of the time) is governed by the AI during combat. However, these characters still have inventories and can level up, and are therefore first class party members in every respect except for the ability to give them direct commands. (Note that the remakes of this game changed the way this work; non-hero characters can be given individual AI settings, and Follow Orders (which lets you control them directly) is now an option; you still can't control UCs, and a certain merchant will still sometimes goof off and disobey your orders (with comedic, and sometimes quite helpful, results).)

Also, how do you handle games where the main character leaves your party at some point? (Yes, I have seen this happen.)

Not to mention that the term 'JPC' entails a spoiler. On a blind playthrough you never know which character can join you, and game plots often spring surprises on you in the form of "strange bedfellows". So they can be called JPCs only in retrospect. Before that, they are all NPCs.

I think you have both made this more complicated than it needs to be and also not addressed all possible situations. In Final Fantasy Tactics you have the protagonist Ramza plus a bunch of variants on characters joining your party:

- controllable story characters: Delita, Alma, Orlandu, etc;
- random mooks you recruit at cities and monsters you convince to join your party; and
- uncontrollable friendly story characters (at least one battle with Algus, Rafa, Malak... these usually are some sort of rescue/escort missions and the uncontrollables are the escortees)

Note that your naming scheme may mean both the random mook and Delita fit as JPCs even if they are fundamentally different and no character fits your definition of an APC. Good question. We don't even need to go far for an example of that. Chrono Trigger is an extremely known game where that happens.
I agree with all your assessment.

NPCILF

Why not just call them AFGNCANAP?

Or Ageless, Faceless, Gender-Neutral, Culturally-Ambiguous Non Adventure Person, for short?