The plight of live service games like World of Warcraft is that they can't always be up and running. Sometimes emergencies happen, but more often than not, downtime is due to regular maintenance.
Is WoW down?
At the time of this writing, all servers are back online.
Is WoW down for maintenance?
World of Warcraft was down for maintenance this morning. Blizzard runs maintenance every Tuesday, generally from 10am ET to 11am ET.
It's a necessary evil to ensure that the servers are running smoothly. Most companies, Blizzard included, will do their maintenance on Tuesdays, which partly owes to the phrase "Patch Tuesday." But, sometimes players can forget this, or maintenance gets extended, and we invariably begin to wonder if the game is down for unexpected reasons.
Companies will usually try to pick a less populated time to perform regular maintenance, so the least amount of players are impacted. But with live service games, there's always a going to be someone online that will be inconvenienced.
For more World of Warcraft goodies, check out What are the Dragonflights in WoW? – World of Warcraft lore, explained on Pro Game Guides.