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Raids : More than 5-man Dungeon Runs. Refers to the game settings where a Party = 5-man and Raid = more than 5-man (usually combinations 10, 20, 25, 40).

Addons for Raids that guilds usually insist on :

CT_Raid
KLHThreatmeter
Decursive

Guilds many also use DKP addons (Dragon-Kill-Points, go check wikipaedia or google for meaning) for loot.

bonto, might be worthwhile to spend a few days reading the WoW FAQ site. Or a week. Yes, it may take that long.

no, decursive no longer works as it used to. the message just shows but when you click on it, it just targets the person. you still need the spell on one of your hotkeys.

probably won't get fix either since blizz already said that they don't like it.

one that i currently like recently is ArcHUD. Luve the rings around the char. Althought sometimes still forget to check health bar.