Its about as simple as the admins can put it.
They are transfering information from one server ( computer ) to another server. ( Hence, they are moving servers. )
You may not be able to access your account details / information / cpanel due to the moving of files from point A to point B.
If you are having troubles entering your site, please post in the correct section of the forum, and explain to the staff the troubles you are having, and your Cpanel name, so they can look up your account information and try their best to assist you.