A Faction, or Side is a group of players or AI working towards the same goal - typically to defeat the opposing Side. Typical missions involve at least two Sides fighting against one another. Additional Sides may be allied with one of the main two Sides in a mission, or they may be completely self-interested.
The vast majority of our missions, whether Cooperative or Adversarial, feature only two Sides fighting one another. In most cases, these are BLUFOR (an American/NATO/western force) and OPFOR (a Soviet/Russian/eastern force). Less commonly, OPFOR vs. OPFOR missions pit two forces using Soviet equipment against one another. BLUFOR vs. BLUFOR missions are exceedingly rare, if they exist at all.
Additionally to the two primary Sides, a distinct minority of missions feature INDFOR, a self-interested force that is not politically aligned. INDFOR may use more esoteric equipment, and are typically less well equipped than the primary Sides. PMCs are considered INDFOR, but are typically very well armed (though smaller in numbers). INDFOR vs. OPFOR, or INDFOR vs. BLUFOR, are the most common combination in two-sided missions.
There are missions that involve three or more Sides. Many of these are Adversarial missions, where OPFOR, BLUFOR and INDFOR are pitted against one another, with each Side having its own agenda and modus operandi. In Cooperative missions, it is more common to see two BLUFOR sides against an OPFOR side, where the BLUFOR sides cooperate with one another to some extent but are not strictly subordinated to one another.
Finally, there are Zombies (or "Rioters" in some scenarios). This disorganized force is inherently hostile to anyone but themselves.
Typical Sides
Missions may feature any of the following Sides (typically two, sometimes more):
BLUFOR
The BLUFOR ("Blue Force") Side may be the Americans, NATO military, or other military forces using American/European equipment or politically leaning towards the West. German, British, Australian, and even Israeli forces, among others, are all considered "BLUFOR". On occasion, the term "BLUFOR" may simply refer to the Player-controlled force in a Cooperative mission regardless of what equipment it uses.
This Side is the most common Player-controlled Side, and is rarely seen as the AI-controlled opponent. It will almost always be fighting against OPFOR, INDFOR, or Zombies. In a few scenarios, two BLUFOR Sides may be present who will normally cooperate with one another, although their command structures are separate.
BLUFOR has several aircraft models available, and will normally have some sort of Air Support. Their Tanks and IFVs are somewhat more combat effective than similar OPFOR vehicles due to high technology optics and similar systems, but are more scarce. BLUFOR tends to rely on Light Vehicles and Transport Helicopters to move troops from place to place, with far fewer APCs and similar armored vehicles.
The OPFOR ("Opposing Force") Side may be the Soviet Red Army, other Warsaw Pact military forces, or any other formal military force using Soviet equipment. The Chinese, Iranians, and other non-western armies (known as "CSAT" in ArmA 3) are typically called "OPFOR". The term may also be used to refer to any AI-controlled opponent Side in Cooperative missions, regardless of what equipment it uses.
OPFOR is typically the enemy AI-controlled Side, although Player-controlled OPFOR is not rare. OPFOR may be pitted against pretty much any other Side, and is often seen fighting another OPFOR Side (in which case the Player-controlled side may be called "BLUFOR" simply to avoid the confusion).
OPFOR has a wide variety of armored ground Vehicles available, particularly an array of different Armored Personnel Carriers and IFVs. Their vehicles and equipment are built for effect rather than comfort, which can be a disadvantage when players must operate that equipment. Its air power is highly effective, but less numerous.
An INDFOR ("Independent Force") Side may feature Insurgents, PMCs, or any other paramilitary/unofficial force. They are typically self-interested, and may by hostile, friendly, or neutral towards any other Side in the mission.
Independents may use any equipment or even combinations of equipment from different manufacturers. Guerillas and insurgents are often equipped with very low-tech gear, whereas PMCs are typically well-equipped. They may outnumber the opposing sides or be tiny in comparison, all depending on the parameters of the mission. Armor and Air Support is usually missing entirely for INDFOR, who more typically use armed civilian vehicles (Technicals) for transport and fire support.
Missions involving INDFOR are very rare compared to BLUFOR vs. OPFOR missions, but historically were more common in Adversarial missions. In scenarios featuring AI-controlled Civilians, INDFOR members may have the advantage of being able to disguise themselves as civilians, to evade, observe, and attack the enemy by surprise.
Zombies (also sometimes called "rioters") are a unique type of force featured in a specific type of mission. They are unaffiliated with any other Side, and will in fact attack anyone who is not part of the Zombie side. Zombies are always AI-Controlled.
Zombies do not use weapons (even if carrying them) nor vehicles. Instead, they walk, run or crawl up to the enemy and attack by clawing and biting. The missions are typically designed in such a way as to allow the Zombies to get fairly close before the enemy gets a chance to react with weapons, such as shrouding the landscape in fog or playing during a moonless night.
The primary advantage of Zombies is their numbers and ability to form hordes. Their numeric superiority allows them to slowly whittle down the opposition, deplete their ammunition, and eventually overwhelm them.
Other Sides
The more esoteric missions feature a variety of other Sides that are too unique or rare to generalize about.
One such Side is the Police. They are tasked with patrolling the map and stopping players from killing one another - although this is open to a lot of interpretation.
Civilians, when they appear, may also be considered a Side. They are AI-controlled, and do not typically use weapons at all (although in some scenarios they use a script that allows them to throw rocks). In most cases when they appear, Players are instructed not to kill them if at all possible (though again, this rule is not always entirely respected).
Hostages and VIPs are another unarmed side, primarily player-controlled. They are mostly tasked with surviving the scenario, or finding a way to link up with one of the "primary" Sides who is looking for them. Depending on the personality of a player playing a Hostage or VIP, they may end up doing something completely unexpected, aligning with the "wrong" side, or any other outcome. As players, they may even become armed at some point during the mission, if they can secure a weapon without being noticed.
Finally, as with everything else, there may be other exceptions.