Charm

For the "threatened" caveat of this spell giving a +5 to its save, does threaten refer to the mechanical term that is used throughout PF that is a check of distance, weapon type, and intent, or is it intended as a more general, could have hostile intentions from somewhere on the battlefield, term?

it is not just the rule for flanking, it is for any obviously aggressive actions made. the point of the spell is to magically make them consider you a friend, and if they are suddenly being treated as an enemy they would get a save.

I am concerned with the initial save and if it requires the "threatened mechanic" to trigger the plus five. It sounds like you are talking about additional saves.

I think it means threaten in the normal non-PF sense and not the AOO sense.

ah i think i understand now, i believe that would be up to the GM. If i am getting your original question, is that if the target in question would get the +5 bonus even if they are not being 'threatened' (eg. by one of your allies standing next to them with a longsword) but just in a situation where combat is going on around them and they may be a target of one of your allies. I can see the following possible scenarios.

A) a bard is invisible and casts charm person on a guard.
I believe this would be the situation in which they would definitely not get the +5

B) a bard is visible and walks nonchalantly up to the guard, then casts charm person on him.
I believe the guard still would not get the +5 save.

C) one of the bard's allies is rushing at the guard, weapon drawn, obviously about to attack.
I think this instance the guard would get a +5 to his save.

D) there is only 1 guard, it is the middle of combat and one of your allies has already attacked the guard.
i would think in this instance the guard would get a +5, because there is already combat, and it would be obvious that all your allies aggressive focus would be on that one guard.

E) (and i think this is the one that relates to your question) there is a large combat going on with multiple people on either side.
In this instance, according to charm person description, i believe the guard would get a +5 only if he were being 'threatened' as per AOO rules, because it is too difficult to say what each character is concentrating on at the moment the spell is cast. the ranger may have just shot him, but maybe the ranger is now about to shoot another guard who is attacking the cleric. but who knows, maybe the barbarians turn the guard threatening the cleric gets crit and split in half, and the ranger will go back to shooting your charm target. there is really no way to know outside of turns, except for the AOO rules.

but to answer your question, i believe the intent was you or your allies appearing to be an obvious threat in some way, they would get a +5 to the save. not just the AOO rules definition of threaten.

E) I'd say in the middle of a big fight everyone feels threatened in some way so in the middle of a fight everyone should get the +5.

I was recently having a discussion about this with my local PFS group. The general consensus was that the use of the word "threatened" means what it means elsewhere in the book; in a square into which an enemy threatens with melee weapon. The problem comes near the end of the spell's description, which indicates if the target is threatened (that word again) the spell immediately ends. So, basically if cast on a target adjacent to an ally with a dagger in hand, the target gets a +5 to their will save, and if the fail their save, the spell immediately ends.

Or we can just interpret the use of the word "threatened" in the spell's description the way normal people do, and not as a strictly defined game mechanic.

I also support the use of the word 'threatened' refers to its use in normal conversation.

"Do what we say, or we'll break your legs!" is a threat.

It remains a threat, even when the speaker is not within melee reach.

"Do what we say, or we'll lynch you when we get to the trading post." is a threat.

It remains a threat, even when the punishment is not imminent.

I'd also extend the intent of the rules, to include threats made against persons and institutions the target holds dear.

So, I'd give the +5, if the PCs kick in the door, start stabbing NPC guards, and try charming the one guy at the back the PCs couldn't reach.
So good luck bargaining with a charmed individual, while holding a knife to their friend's throat.
No joy on "Do what we say, or we'll burn your house down!", even if it's unoccupied.

Does this make it harder to use? Yes, but it's supposed to be a subtle spell. It's not designed so an NPC will say "Wow, you're my new best friend forever. By all means, disembowel my dear, aged mother. She means nothing to me. Why should I care?"

My favorite scenario is trying to charm someone standing opposite a firing squad. Though under those circumstances I might be tempted to just fail my save voluntarily.

My initial inclination is that it should be used purely mechanically. I can still see subtle uses in the middle of a large scale battle e.g. swords and arrows flying everywhere, but I find a lone soul and convince him that he is being mislead, used, tricked, etc.

After reading this I suppose I might be open to a bit more DM fiat. Ultimately I would like to see an official rule for society play, but I can understand not making an official rule on every little thing. Sometimes nitpicking the rules can detract from the fun.

Heresy! True fun can only be achieved when the rules are thouroughly nitpicked! Burn the practicers of badwrong fun!

The 'threatened' phrase was in the description of Charm Person from 1st edition, so does not rely on the 'threatened squares' concept which only appeared in 3rd edition, more than quarter of a century after Charm Person was written.

Heresy! True fun can only be achieved when the rules are thouroughly nitpicked! Burn the practicers of badwrong fun!

Sorry, but you're not gonna charm anyone while threatening to burn them. :p