Servers
A server is actually a physical computer that handles "clients," or other computers. In the case of "Need for Speed: World" online, a server created by game creator, Electronic Arts, handles traffic from incoming players. It's this computer that you're getting disconnected from when you receive the "Disconnected from Server" error.
Server Overload
One possible reason you might experience the "Disconnected from Server" error in the game is server overload. Servers can only handle so much traffic, and when too many people are connected to the server, it may get overwhelmed and shut down. Additionally, users may be kicked off the server during updates by E.A. During these updates, users can't be on the server because different parts of it will be shut down and rebooted.
Running Older Version
Another potential problem could be that you're running an older version of "Need for Speed: World," in which case your connection to the server may be compromised. Your computer sends communications to the "Need for Speed: World" server via the Internet, and if the server is running a newer version of the game than the version you're running, communication problems could arise. The game code on the server must match the code on the version of the game you're running, otherwise you may experience a glitch or a bug that causes you to be booted from the server.
Possible Solutions
The first thing you should do is to visit world.needforspeed.com and download any patches to the game. If the problem persists, uninstall the game, and then download and install the newest version of the game. However, if it's a server issue, you may have to wait until the problem is resolved by E.A. Check the forums on the website for any information regarding bad servers or patches. If a patch is being installed at a certain time, try reconnecting to the server after the designated maintenance period has expired.