Damage indicates how much heart damage the item does when it strikes an entity such as a mob or another player.

Here is the format for adding mob damage to your item:

damage[0] = 2;

One damage is half a heart. So, for example, an item that deals one heart's worth of damage would have this value set to 2. If you wanted it to deal three and a half hearts, the value would be 7, and so on.  The defualt damage when no code is present is 1. 

See Also