Full servers: based on total population or current players logged in? Supposedly server statuses will bounce between high and full, though I am unsure if that is based on people transferring on and off or just players online.
Please include reference from anet if relevant.
Best Answer
Official source from 'CC Eva', a community coordinator:
This means that the number of accounts with the server as their home server has reached the capacity cap set for that server. Over time if people move away from the server it will become available again for new accounts to choose as their home server.