What's a 'Creep'

[:1]I've searched high and low but no one's explicity said what a creep is, I have rough idea that it's an expansion defended by units but I'm not entirely sure. Could someone outline what it is? And what creeping is?|||Creep: Unit owned by a Neutral Hostile computer (not a player) found in the terrain.

Creeping: Leveling your hero by fighting creeps so you have sufficient power to combat enemy player units when your heroes meet them in combat.

For more, see: http://www.battle.net/war3/basics/creeping.shtml|||on the minimap they are denoted by the spots of green, orange and red, green being the weakest and red being strongest. creeps guarding goldmines typically belong to the orange range except in a few maps.

Also, the term creep-jacking is to mean that you engage the enemy while you catch him creeping.|||You can also purchase some of those creeps from mercenary camps in some maps.