TERA PC servers will be merging on September 18th. The merger is to provide players with a larger community to make grouping faster and more efficient for dungeons, PvP and to provide players with a "more bustling in-game economy". There will be one PvP server, one PvE server and one PvE RP server.
To make sure players can choose where their characters end up after the merge, En Masse will open free character transfers between server types (PvE -> PvP/RP etc.) from September 4 – 17. Players won’t have to do anything ahead of the server merge – all character, guild, friends lists and more will be copied to the new server automatically. There will be a cap on the number of total characters players can have on the newly created sever, however En Masse will be providing additional character slot unlock coupons to help make room for players with characters on multiple servers. These character slots will be given out to all accounts that log in the week prior to the merges from September 11 – 17.
Head to the TERA site to read more specific details and a handy FAQ.