A
biological implement of the
Zerg in the game
Starcraft. It is so called because it
slowly "creeps" forward over time.
A Zerg colony relies entirely upon the creep. The only structure that can live independently is the hatchery. Zerg drones can build a hatchery on bare ground because the Hatchery itself is a creep colony. There are only two types of creep colonies - hatcheries and smaller creep colonies; smaller creep colonies still require creep to be contructed, however.
The way a creep colony works is simple. Inside the colony it produces spores in the liquid chemical it stores. It pumps the spores up through a tube and as they travel it fertilizes them. They then reach the "mouth" of the colony and it expels the spores into the air. They then settle on the ground nearby, and begin to germinate. Once they start to grow a purple biological layer covers the ground like a skin. It roots itself into the ground and absorbs the nutrients from it. As the creep grows the creep colonies expel their spores further and further away, until they have expelled them to the maximum distance possible, then they repeat the process from close by again. If a creep colony is destroyed and it cannot supply spores to the creep, the creep will die and recede.
Constructs built on the Creep root themselves into it and not the ground. This is because they require nutrients, however can only use one type. The creep works by converting the nutrients found on any planet into the same nutrients found on Char (see Zerg), so that no matter where the Zerg are they can still spread. Originally the Zerg did not rely on this Creep, however once the Zerg started to spread and structures could not survive on the foreign planets, the Overmind created this creep.
As the creep is biological, it is soft and spungy and unstable. As such, foundations cannot be laid and any Terran or Protoss contructs would simply collapse if built upon the creep. Hence, the Terran and Protoss cannot build constructs on creep. This limits the Terran and Protoss in Zerg land, however it is a double edged sword, as the Zerg cannot build without it, hence will find it difficult to impede on Protoss and Terran ground.
Reply to Mr100percent: Not all buildings spread the creep, only hatcheries and creep colonies.