It came from the Blog, for example, is the WoW Insider guild on Zangarmarsh (US-PvE-H). We have monthly events as well as weekly dungeon runs. It's also a casual leveling guild for in between blog-sponsored activities for readers to hang out together. So we're a fan guild plus an event guild plus a helpful leveling guild.
I belong to another guild on a different server that is a 25-man raiding guild with a severe case of altititis on the side. Non-raiding players are fine as long as they're good guildies. Many raiding guilds, however, want only players who are available to raid or are getting their characters raid-ready ASAP.
Casual, hardcore, roleplaying, PvP, social niche, themed, mature as in adult themes and language or mature as in adults who keep it clean, kids allowed, kids encouraged, no kids ever -- there are so many different ways to describe a guild. How would you categorize yours?