- An organism not native of Earth. Also known as an Extraterrestrial. Also used as an adjective to refer to anything that's not Earth in origin.
- An Abbreviation for Armour Piercing.
- This type of ammunition is a shell filled with a dense material which is capable of breaching most types of hardened armour. Despite its name, it is the damage type that most commonly does nothing to heavily-armoured aliens, and actually has no armour-negating qualities at all.
- An abbreviation for Area of Effect. Used to refer to attacks that affects large area of the map, usually explosions. Also used as a term to measure how large the area of effect is.
- A soldier of X-COM specializing in underwater operations. First appeared in X-COM: Terror from the Deep.
- The name given to the controlling being upon Mars. Also known as the "Alien Brain".
- The highest rank an aquanaut of X-COM can attain. May also refer third highest rank a soldier of X-COM can attain.
- The highest rank a soldier of X-COM can attain. May also refer second highest rank an aquanaut of X-COM can attain. May also refer to the main leader of X-COM or just its many sector/regional branches such as the one in charge in Mega Primus. May also refer to the highest ranking alien X-COM can capture.
- The name given to a region of Mars. For the game's purposes, it is the site for the alien's main headquarters.
- E-Mail X-COM
- A cut down and very simplified play-by-e-mail combat game with the X-Com theme.
- Enemy Unknown
- The original release (UFO: Enemy Unknown), Playstation version (X-COM: Enemy Unknown) and the re-imagined remake's (XCOM: Enemy Unknown) subtitle. Also known as X-COM: UFO Defense in the United States due to copyright issues. Used to refer to the first game of the franchise. May also refer to the new upcoming remake.
- The titular combat android player character of the X-COM third-person shooter X-COM: Enforcer. Also used to refer to the game in general.
- A portable and persistent light source that activates when it hits the ground after being thrown.
- An abbreviation for Enemy Unknown.
- Foundry is a base facility from the New XCOM Game that allows you to upgrade your weapons and technology.
- A thrown area-effect weapon consisting of an amount of high explosive substances encased in metal fragments with a timed detonator. The Grenades used by X-Com are all equipped with a timer and a trigger safeguard mechanism that prevents the grenade from detonating after the timer has elapsed and only when it lands on the ground.
- Short-hand for Ground Zero. This is the point at which an explosive is detonated; the center of the blast area. Distance from Ground Zero is referred to in radii. The edge of the blast area, where damage is minimal or none, is referred to as the Blast Radius.
- An abbreviation for High/Highly Explosive(s).
- Heavy Weapons Platform
- A miniature unmanned tank.
- HE Block
- A property of most walls and many terrain objects that causes them to resist or block explosive blasts.
- An abbreviation for High Explosive Block.
- High Explosive
- Used as an adjective to refer to any object or item in the game with explosive properties or properties that affects explosions. It is also a damage type calculated in the game along with Armour Piercing (AP), Incendiary (IN), Laser, Plasma and Stun. May also refer to the High Explosive inventory item from the first game.
- An alien based HWP that uses hover technology for locomotion instead of the traditional tank tracks or wheels.
- An abbreviation for Heavy Weapons Platform.
- Short for Incendiary.
- A combat aircraft designed to intercept and shoot down other aircraft. The name of the fighter jet first available to X-COM. May also refer to the X-COM flight simulator game X-COM: Interceptor.
- A damage type that causes health damaging fire to spawn in its area of effect or set unfortunate units to be set on fire and sustain damage each turn.
- Kiryu Kai
- An elite team set up by the Japanese Government that failed to deal with the alien menace before X-Com was formed. Spirit Dragon Society? Energy Dragon Association?
- A light pump; A weapon technology involving highly concentrated beams of light.
- Laser Pistol
- The first laser weapon in the laser family. In effect, a laser sub-machine gun.
- Laser Rifle
- A popular and very well balanced rifle based on laser technology.
- An elongated and much improved Hammerhead. The equivalent to the Avenger on TFTD.
- Short for Line Of Fire.
- Line Of Fire Template. A series of pixelated templates used by the game to represent a pseudo-3D form on the battlescape.
- Short for Line Of Sight.
- The greek letter ψ Commonly used to refer to the field of Psionics
- Psionic Amplifier, used by humans to amplify and channel their psionic abilities
- An electronic hallucogenic implant with a considerable bounty.
- the art of invading and manipulating the psyche of enemy targets through sheer willpower
- Phosphorus - a poisonous and flammable substance that reacts when exposed to air, used in Incendiary munitions and chemical flares.
- Used to indicate how high a soldier is within X-COM's hierarchy. Higher ranking officers provide morale boost in combat while causing morale penalty should they die in combat. May also refer to a captured alien's rank; what kind of intelligence is gathered through Live Alien Research depends on the interrogated alien's rank.
- The lowest rank a soldier of X-COM starts with after hiring. Often used by players as cannon fodder and/or decoys/distractions. If the rookie survives the first mission and attain a higher rank, the newly promoted squaddie is usually put into more important roles.
- Stands for Super Heavy Infantry Vehicle. A series of Heavy Weapons Platforms XCOM operatives used in Enemy Unknown (EU2012).
- The aquanauts' equivalent to the land based soldiers' rookie.
- The name of a slow VTOL Russian troop transport aircraft that can remain in the air for days on end with a single tank of fuel.
- Submersible Weapon Systems. Underwater variant of HWP
- Terror from the Deep
- Used to refer to the second X-COM game X-COM: Terror from the Deep.
- Terror Mission
- A type of alien mission with the goal of terrorizing a populated area. A type of X-COM mission with the goal of stopping the alien terrorists.
- Terror Site
- A city that is being attacked by Alien terrorists.
- Terror Units
- A special alien unit that only appear in Terror Missions and other significant missions. The type of Terror Units that will appear depends on the primary alien species they're accompanying.
- An Abbreviation for Terror from the Deep.
- Time Unit
- A time unit is a fraction of time taken by any unit to perform any action. It's also a measure of speed; how fast a unit can do things in a single turn.
- An abbreviation for Time Unit.
- An abbreviation for Unidentified Flying Object. Used to describe any unknown flying object in real life but is used in the games to refer to alien spacecraft in general regardless if it's known or not.
- UFO Defense
- The name of the US release used to avoid possible copyright conflicts. Officially changed to Enemy Unknown as of the 1.4 update.
- An abbreviation for Unidentifid Submersible Object. An amphibious UFO. The term is commonly used to reference the alien subs in TFTD, but does not appear in that game. Presumably coined by players, it has been used in official game publications.
- Stands for Vertical Take Off and Landing. A capability of most X-COM aircraft which allows them to achieve flight without requiring a long airstrip to take off and also saving the underground base some space.
- The non-hyphenated version of "X-COM". This version is now used in current generation X-COM games such as the The Bureau: XCOM Declassified and XCOM: Enemy Unknown.
- Short for Extra Terrestrial Combat Unit; A paramilitary organization bent on defending humanity against alien threats and using their own advance technology against them. Is also used to refer to the franchise as a whole, especially the earlier generation of X-COM games.