Unmanaged - You do EVERYTHING with the server yourself excluding hardware replacements/troubleshooting.
Managed - Some predetermined level of support is provided on the server. Which may include but is not limited to: software installation, troubleshooting, account creation, server monitoring and log monitoring.
Originally posted by vriley What is the difference between managed and unmanaged dedicated servers?
Note that providers seem to have their own definitions of the term 'managed' and that you should carefully look over what is (and is not) provided. There are some 'managed providers' who seem to offer very unmanaged services.
Also note the different between 'managed' and 'semi-managed'. With 'semi-managed' servers the various tasks done for you are limited. The same is true with 'managed'; however, there are fewer tasks done for you with 'semi-managed'. Always be sure to check out what tasks your providor (or future/possible providor) will perform for you.