StarCraft is based on collecting two different kinds of Resources: Minerals and Vespene Gas. They differ through their gathering mechanic.
Minerals are - among other uses - used for basic buildings and workers. These units only cost minerals. An increase in mineral income can be achieved by improving the saturation of the Mineral line by adding additional workers. When minerals are mined out, the patches vanish entirely. Read more about ideal mining.
Also called "gas", it is mainly used for higher tech units and is especially important in late game situations. There are no units that cost only gas. Gas has a linear rate of gathering - the gas gained from each geyser is constant over time and does not benefit from adding workers beyond the optimum number. Professional maps yield maximum gas (about 288 gas per Fastest minute) with three workers per geyser, while other maps need four or even five. As a result of the constant rate of gain, improving your gas income usually requires additional bases. Once the initial content of a Geyser has been emptied, in quantities of eight gas, it becomes "depleted" and the sprite of gas decreases in size. It can then be mined, with 2 gas per worker trip at the same frequency as before, for eternity.
Players can create and defend additional bases known as Expansions throughout the game to secure more resources, while at the same time attempting to stop enemy players from doing the same. In Starcraft, map control is usually synonymous with resource control.
The production of almost every unit requires an additional resource: Supply. The amount of supply can be increased by the building of certain buildings or units.
Building either of these will increase the amount of supply a player is able to spend. The maximum amount of food for any player is 200. Due to the economic inefficiency of building Command Centers, Hatcheries or Nexuses for supply, these are generally not built for this purpose alone. It is worth noting that Supply, Control, and Psi, for Terran, Zerg, and Protoss respectively, are treated as separate resources in-game. By having control over each race, you can build 200 supply's worth of units for each race you control.
The term "Supply Block" or "being supply blocked" usually means "18/18" or "36/36" Supply (e.g. "92/92", "134/134", "182/182" and so on).
Note: Supply is sometimes called Psi for the Protoss and Control for the Zerg. Another general term for supply is Food.