"Managed" service, generally speaking, means that
the provider supports the configuration.
The support may take the form of "Graphical Interface"
(control panel) or, for more advanced plans,
it may involve the provider's engineers configuring
and upgrading all installed software (e.g. databases,
web server packages, kernel, etc).
"Unmanaged" service, in simple terms, means that you
are on your own in terms of configuring and maintaining
the server. That may be just what you need if you
have experienced engineers on staff.
"Umanaged" services typically still allow you to call
on the hosting provider's engineer staff, but at
a steep hourly rate (we haven't seen anything below
$150/hr for high-end server work).
Needless to say, "managed" services cost more than "unmanaged".
When selecting your ideal web hosting plan, make sure you
understand who is going to be responsible for
managing the different components of your service.
COOL EXTRAS
Your provider may offer advantages that are not normally
considered part of "web hosting" service, but may nevertheless
be important. For example, some large web hosts located
in urban/sub-urban areas rent out
conference rooms for meetings with clients.