Star Wars: The Old Republic has been making a move toward fewer servers with higher populations for a while, but tomorrow's maintenance is the final step. After character transfers earlier in the year and the higher-population technology rollout, the server lists are being fully merged as of tomorrow. If you still have characters on a locked server, they will be transferred over to their new home tomorrow whether you like it or not.
For those players curious about their new destination or the ever-present naming issue, the team has created an FAQ to answer any obvious questions. The character limit on the destination servers has also been raised to 12. Players who have more than 12 total characters after consolidation will still have access to all of their characters but cannot create any new characters until they delete a few (although all of the characters will be available for play). As with any sort of transfer, there's still some ambiguity about how smoothly everything will run, so players will have to keep their eyes peeled, log in tomorrow, and see what happens after the dust settles.
[Update: The team also just released a miniature dev blog that explains how shadows will soon be prettified.]