Stacking refers to a number of overlapping bonuses or other effects on a unit. Each of the effective bonuses multiply on top of each other.

For example, a unit stands near enough to a healer's aura to receive ongoing health replenishment. If that unit stands close enough to four healers, then the healing effect can be four-fold. In other words, the effect of these healers stacks when they're close enough together. Conversely, a unit might receive multiple bonuses: attack strength, healing, or shielding by standing near to different units with different auras. The combined effects of these auras stack on any unit within range. A classic example of stacking can be found in Dawn of War's Ork Mob Bonus.

Some games might prevent bonuses from stacking for balance reasons. Healing rates might be capped to prevent fighting units from becoming invulnerable. Some powerful bonuses might be exclusive, meaning that all other bonuses are disabled when they are active. Again, this is designed to prevent units from becoming too powerful or having an "exploit" where unscrupulous players can invoke these bonuses for easy wins, time and time again.

Or Statistics. All units are defined by a string of numbers that describe their attributes and weapons, perhaps even a few magic spells tucked up their sleeves. They're more like the computer controlled characters you encounter in a role-playing game (RPG). Each one is defined by a set of stats and rules that determines how it behaves and moves, and when large numbers of them clash the game is furiously looking up character charts and doing the sums just like human players did in days of old. Everything now takes place in milliseconds, not hours; and modern RTS game engines are running cut down physics models rather than emulating old abstract, turn based games.

	Health (or Hit)		All units have Hit points of some kind or another. Its their most important attribute: if all their Hit points are lost, the unit dies or explodes. In practically every real time strategy game you'll get a graphical indicator called a Health Bar to let you know how your unit is faring. Units are granted a certain number of points when created and lose them when injured or damaged by the enemy. Health won't replenish itself, unless a specialised support unit (like a Medic or a Mechanic) can attend and replace those lost points. Some units have the ability to self-heal themselves at a slow but steady rate.
	Attack		Any unit that can attack another uses Attack points to measure the amount of damage they can inflict. At its simplest, an attacker is using Attack points to subtract Health points from its target equal to its Attack. Naturally, its usually a lot more complicated than that. Whether its a laser beam, a stream of bullets, an arrow, a fireball or a spurt of venom, an attack is little more than just a number and a set of little rules to determine how it subtracts those health points. Sometimes you'll see small numbers floating up above a battle indicating how much damage has been inflicted on whom. When you look up the rules that determine how units attack and defend each other, it becomes fiendishly more complex. Attacks are affected by a range of other stats, such as upgrades, armour, energy shields, firing range, splash damage and a host of other variables.
	Movement		Movement in an RTS unit is different from the old strategy game. Turn based games often worked on a map subdivided into a grid, where a unit moved x number of grids per turn. In real time, units are animated and move anywhere they like on the map (although they still tend to stop and start in a suspiciously grid like formation on the map!). Movement usually refers to a unit's top speed.
	Acceleration		This is how fast a unit can speed up or put on the brakes. Light units like infantry can jump into a full run in next to no time; a heavy tank might take a while to get up to speed. This directly affects the responsiveness of units.
	Turn Rate		The speed at which a unit can rotate. A marine or a moon buggy might spin on a dime, while a battleship might take half a minute to orientate itself.
	Reload Time		The speed at which a unit waits between firing a shot. This is the time it takes to "reload" a gun or let a laser "cool off" between shots. Some units fire quickly like a machine gun; other very slowly, like heavy artillery. Some might have to wait for an energy bar to replenish itself before firing again.
	Range		Visual range is just how far a unit can see. Weapon range is how far it can target something. A unit can't do anything against anything that sits outside visual range - on its own, that is. All your forces share a collective vision: what one unit sees, all others can too. Some units, especially artillery pieces, can shoot very long distances well outside their visual range, but require a second unit to move up ahead to see the target first so it can be auto-acquired. The rest is automatic!
	Armour		Units do have some defenses against attacks, and sometimes there's a stat representing the amount of armour a unit wears. Often, armour is just a modifier, a number that changes another, like an attack. At its simplist: an attack is reduced by the armour modifier before it can affect the unit's health. Armour tends to be the sort of thing you get with researchable upgrades and techs. Units do have some defenses against attacks, and sometimes there's a stat representing the amount of Armour Points a unit wears, just like a second set of Hit Points. Often though, Armour is just a modifier.As an alternative to being a modifier, Armour points might simply be a second set of health points for your unit, except if armour points are zeroed the unit is simply naked, not destroyed. In this case, armour points might have to be drained first before health is affected. Unless - (still with us?!) the weapon in case is armour piercing in which case it might still affect health points before armour is exhausted. Give game developers an inch and they'll take a mile! Armour tends to be the sort of thing you get with researchable upgrades and techs.
	Shields		Another form of unit protection is that of an energy shield or force field. Shields aborb most or all of the damage before unit health is affected. Shields can be completely lost without injury to the unit and recharged later. See Energy, below.
	Energy		Some units have a resevouir of points that are used to perform special functions outside the usual Attack, or some kind of defense (like a force field) that uses up energy points before it starts to subract hit points. The usual convention is that energy slowly replenishes itself on its own, whereas health points won't. Spellcasters or special weapons may require a large chunk of energy just to fire, and then can't fire again until recharged. Energy can also be interchangeable with Fuel, Health, or Shields.
	Fuel/Ammo		Normally units don't eat, sleep, rest or run out of juice. They're just as strong and perky staggering around on one hit point after ten battles as they were when they first popped out of the factory. But some games go to the effort of modelling fuel or ammo consumption, adding an extra strategic dimension that forces the player to maintain supply lines and an Achilles Heel for their enemies to exploit.

A way of simulating the amount of supplies and materials "consumed" by your units. This is very similar to Population Limit, except Population Limits put a cap on the number of units you can build: i.e. one population point is used to build one unit; whereas support describes how much a unit costs to run. Small units like infantry may only consume one point; giant units like tanks or battle-cruisers may gobble up several.

The Homeworld sequel Cataclysm makes obvious use of Support Units. You can build a lot of small strikecraft but only a few giant warships, and even then, you are forced to spend a lot of resources just increasing your capacity by constructing Carriers and adding Support Modules to your Capital Ships. More info.

1.) A unit that, when used in conjunction with other units, increases those other units' capacity to perform. A support unit may not be able to achieve much on its own, but its presence when mixed with a group of regular fighting units might prove to be decisive. The classic example is the medic, an unarmed unit that heals any friendly units nearby, keeping them alive longer in a fight, effectively preserving the strength of the group.

2.) A Military Unit (often a heavily armed one) that covers for other assault units, usually by laying down covering fire to keep the enemy at bay. More info.