The Awake function is called when the script instance is being loaded.

Awake is used to initialize any variable or game state before the game starts. It is called only once during the lifetime of the script instance. It is also called after all the objects are initialized, so you can safely speak to other objects or query them using, for example, GameObject.FindWithTag . Each Awake function of the GameObject is called in a random order between objects. Because of this, you should use Awake to set up references between scripts, and use Start to pass any information back and forth. Awake is always called before any Start functions. This allows you to order initialization of scripts.

private var myTarget : GameObject;
function Awake() {
  myTarget = GameObject.FindWithTag("Target");
}