Servers

From AionSource.com Wiki

A game server, sometimes just called a server, is remotely or locally ran dedicated Server computer used by game clients to play league matches, or in public communities. Any videogame played over the internet generally requires a connection to a game server. See also here.

In Aion: Tower of Eternity, it appears that games purchased from a US vendor will play on US servers, while games purchased from an EU vendor will be played on EU servers. [1]