A full continuously updated list of servers can be found at HammerWiki's List of servers.
A server (also known as shard, game world and "realm" among other things) is one independent copy of the game content, the "world". What this means, is that characters created on one server exist only on that server and will only ever be able to interact with other characters that exist on the same server. As such, groups of people who wish to play together will need to create characters on the same server in order to do so.
Traditionally, MMORPGs have server-sizes anywhere from as low as 1000 players to as high as in excess of 100,000 (an example being EVE Online). Most commonly, however, server sizes seem to range between 2,000 and 5,000 simultaneously online players at peak capacity. Depending on the game, servers may stop accepting new connections, queue players, or simply lag horribly when pushed beyond their capacity limits. How many - and what capacity - servers will be available for WAR is not known at this time.
When choosing a server to play on, it is usually best to pick a server which is as close as possible (barring servers which are overcrowded) to your physical location. Choosing a server close to you will reduce the latency time between your computer and that server, lowering ping and reducing lag.
North American servers supported by BioWare Mythic will be located in Virginia, USA and will service players in Canada, the United States and probably also Mexico. It is possible servers in other North American locations will be established, but this is unconfirmed. North American servers will be available when WAR launches.
GOA was supporting European servers, with official servers dedicated to English, German, French, Spanish and Italian languages. These have serviced players across Europe and probably beyond. The servers were located in a new datacentre; Lille in northern France.
On July 7th, 2010 GOA transferred their servers to BioWare Mythic. These servers are now located in Germany.
EA Mythic will also be supporting Oceanic servers located in Melbourne, Australia. They will service Australia, New Zealand, and other locations in South East Asia such as Indonesia and Singapore. Oceanic servers will launch simultaneously with NA and EU servers.
EA Russia will be supporting Russian language servers, due to launch early in 2009.
EA Asia Online will be launching and operating servers in Asian territories, including China, Japan, and Korea. Additionally, Gigamedia will be servicing players in Taiwan, Hong Kong and Macau. No release date has been announced for these servers.
It has been confirmed that some WAR servers will be set up with alternative game mechanics to cater to the tastes of different groups of players. Common to all servers, however, is that it will not be possible for very high level players to enter low level territory and kill everyone in sight. Currently, the mechanic for preventing this literally turns high level players entering low level RvR (PvP) zones into a Chicken with little or no combat ability. Only these server types have been confirmed:
Players will always be RvR flagged, and able to engage in RvR combat just about anywhere in the game world. Players will be "chickened" when entering a tier zone two notches below them. Ie: Rank 40 (Tier 4) players would be chickened in tier 2 and rank 30 players in tier 1.
Players will be expected to follow additional rules governing character naming and in-character speech. They must essentially roleplay - act as if their character was a real character in the Warhammer World - as much as possible. Roleplay servers will follow the Core ruleset.
These servers follow both the Open RvR ruleset and the additional roleplay rules.