control panel

This is a web interface where you can manage (not build) your website. You can do such things as make email accounts, password protection, ftp users, subdomains, databases, etc for your site.

The most popular web control panels these days are CPanel and Plesk.

Rule of thumb: A control panel is really useful, even if you are an advanced web developer and linux user. I myself would not consider any web hosting that didn't have a control panel.