A managed dedicated server is either one you rent or one you co-locate where someone else is in charge of the well being of the server.
You still have the power of a dedicated server however another indivual or company is in charge of making sure the software is up to date, all patches are installed, and that security is up to par. This leaves you with more free time to work on your website, and leaves you with a piece of mind that your dedicated server is being taken care of.
