Supply

From The StarCraft 2 Wiki

Supply, besides the regular meaning of the word, is what the Terrans must accumulate to support the creation of units. Supply is sometimes also referred to as "food" for the Terrans, and "supply" can also double as "control" for Zerg and "psi" for the Protoss.

"Supply" means in "real" terms the ability to recycle and produce oxygen, water and food, in addition to what individual equipment can do for its user (such as what the CMC Powered Combat Suit can do). It also means stash of spare parts for vehicles, and is just a general term for how much Terran power can be supported on a given area (a single map in the game).

Supply in StarCraft

In the game, Supply is a measurement of how many units a player can control on a specified battlefield (one map). The value of 200 control units is the maximum for a single conflict, and is reached by producing Supply Depots and Command Centers. Different units require different amounts of control, depending on their psyche, so a Marine will only require one point of supply and a Battlecruiser will require 6 points.

If the Terran should lose a lot of supply by having Supply Depots destroyed, any existing units will not be rendered useless. The control is only needed to increase the size of the armed forces, as the army always has a certain amount of tools to sustain themselves for periods of time.