I know of two solutions for this. Someone else might come along with better ideas, too…but…
1) Use your .htaccess file to password-protect your wordpress directory. Then only people you pass the username and password to can visit the site. Everyone else will get a “Forbidden” error page. This is not a WordPress thing – you have to edit/create your own .htaccess files to do this.
2) Install WordPress in a subdirectory, but place index.php outside of the installation, one level up. Make it a static page. Leave only the “login” link of your Meta section on the static page. People who come to your site will see the static page, and can’t go any further into the site unless they log in. This can be done solely with WordPress code, but it’s most certainly advanced theme editing to get it done.
Like I said, there may be other options, but those are the two I know of.