Hit makes it so you can't miss. If you had a 100% chance to miss without hit it would be pretty bad, however you 'naturally' have 92% to hit something so adding that extra 8% makes sure you never miss.

You're stacking hit to offset your character's natural chance to miss. With a base five percent miss rate and then another three percent for boss level enemies, you need enough +hit to bump your hit chance UP to 100%.

The base miss chance against Boss level mobs (level 83) is 8%. If you stack enough hit to get +8% chance to hit then that reduces your chance to miss from 8% to zero.

+hit does not increase your chance to hit.

It decreases your chance to miss.

If you have max weapon skill (400 atm) and you are fighting a lvl 83 mob (a raid boss), the chance to miss is 8%.
Source: http://www.wowwiki.com/Hit_rating#Calculating_miss_rate

Furthermore, the chance to "hit" is never 100%. An attack roll always result in either a "glancing blow", a "miss", a "crit", a "dodge", a "block", a "parry" or a "hit". Against a raid boss, your chance of a glancing blow in melee is always... 24%... I think. I can't remember actually, but roughtly that anyway.

As you are standing behind the boss of course, he can't parry so we take that away from the results. Nor can he block so take that result away also. He can still dodge (6,5% chance) but with enough Expertise that is removed as well.

And you still have your chance to "crit". Let's imagine you have a 40% chance to crit.

So, with 0% to miss, 0% to be parried, 0% to be blocked, 0% to be dodged and 40% to crit, your chance of a "hit" is still only 36% (if my memory served me right about the 24% glancing blow) . All other swings are "crit" or "glancing blow".

WoW's attack mechanics work in such a way that with a 0 Hit Rating, you have a 5% chance to miss your target. This miss % can overcome by stacking Hit Rating. If you read the tooltip for Hit on your character sheet, it actually says that Hit Rating INCREASES your chance of hitting a target that is your by X%. So if you have enough Hit Rating to get 5% hit, you've effectively overcome the 5% miss chance and will (almost) never miss. Of course, the target could still parry, dodge or block, which is what Expertise is for, but that's for another discussion.

The reason why you need 263 Hit Rating to get 8% hit is because raid bosses are considered to be level 83. For each level that a target has on you, you effectively have a 1% reduced chance of hitting that target. So, at level 80 with +0% hit, you have an 8% to miss a level 83 target (5% base + 1% for EACH of the 3 levels that target has on you). If you have 263 Hit Rating to get +8% hit, then you will never miss the level 83 boss.

If you want to see more on how Hit Rating and hit % are related and calculated, see http://www.wowwiki.com/Hit_rating

8% hit just means you have an 8% *increased* chance to hit a boss, because otherwise you'd have an 8% chance to miss.

Like others have said, 8% hit means that you have reduced the chance to miss from 8% to 0%.

It's derived from the difference in your weapon skill and the defense skill of the enemy. You're a level 80, so you have a 400 weapon skill. The boss is a level 83, so he will have a defense skill higher than your weapon skill. That skill difference translates in an 8% chance to miss.

Then you have a bunch of crazy calculations and algorithms for different situations and levels.

But that's the gist of it.

@Madcat

That's not actually how miss chance works there. Your chance to miss level 81 or 82 targets is not 6 or 7 percent (respectively), there is quite a spike to miss once a target is 3 levels above you (or more accurately, once their defense is more than 10 above your weapon skill).

answering your statement about hit, you are adding in the 400 weapon skill and the fact that the target you are attacking is 3 levels higher then you, thats where the other 92% is. Try using a weapon that you do not have max skill against a raid boss, I guarentee you will see your 8% is not 100%