Server

A game server (sometimes host or shard) is a server which is the authoritative source of events in a multiplayer video game. The server transmits enough data about its internal state to allow its connected clients to maintain their own accurate version of the game world for display to players. They also receive and process each player's input. (from Wikipedia)

DDO game servers
DDO currently has 8 distinct persistent game worlds (servers).
 * Argonnessen
 * Cannith
 * Ghallanda
 * Khyber
 * Orien
 * Sarlona
 * Thelanis
 * Wayfinder (used to be a German language recommended server, not anymore)

Additionally, there is one test/preview server: Lamannia. It is assumed that all game servers reside in Needham, Massachusetts.

Each server is a distinct game world. Your characters cannot see or interact with anything that happens on a different server. Your shared bank and the shared platinum vault is also restricted to characters of one server; so is the Auction House and in-game mail. Individual guilds are also tied to a server.

Character transfer
Transferring characters across worlds is a paid service, $24.95 €21.95 £18.95, or 2995 Turbine Points per a character. (see full details here).
 * You only keep your items in your inventory and (regular) bank. You don't get to keep your reincarnation cache and account-wide bank.
 * You may transfer your character as many times as you wish, however, due to a bug/technical limitation, you can't move your character to a server where once the character was on.
 * For example, you have moved your character originally from Thelanis to Argonessen. Now you want to perform another transfer from Argonessen to elsewhere, but this time your choice excludes Thelanis.

Account-wide/across servers

 * Your game account allows you to access/create characters on all live servers, as well as the Lamannia test server.
 * Your Turbine Point balance.
 * The benefits of your account type and account upgrades purchased from the DDO Store (such as adventure packs or premium races/classes).

Server-depentent

 * Your Astral Shards balance.
 * Any perks that you unlock by favor, such as 32 point builds, favor-unlockable races and classes.