Solved Question about HookMethod

Hello everybody,
what is the difference between these two (OnLootItem is only a hook exemple) :

Code:

void OnLootItem(BasePlayer player, Item item)
{
    ... do something
}

and

Code:

[HookMethod("OnLootItem")]
void OnLootItem(BasePlayer player, Item item)
{
    ... do something
}

I sometimes see this [HookMethod("")] but i don't understand it's purpose