Wikimedia Foundation (the organisation that runs Wikipedia) reports that due to an overheating problem in the European data centers of Wikimedia, many of the servers in their farm turned off to protect themselves. As this impacted all Wikipedia and other projects access from European users, all user traffic to Wikipedia and sister project websites were diverted to the Florida cluster of Wikimedia.
However the switch to the Florida servers did not go on properly and caused the DNS resolution of Wikimedia sites to stop working globally. Although this problem was quickly resolved but due to DNS caching effects this problem spread wide all over the world and the downtime in the website became notice-able.
A datacenter is basically a facility used to house computer systems and associated components which run servers that serve your favorite websites. There are recommended ranges of temperature of 16–24 °C (61–75 °F) and humidity range of 40–55% with a maximum dew point of 15°C as optimal for data center conditions. A few months ago we had told you about the music service last.fm shutting down due to datacenter overheating.