Dedicated server is a service where the user leases the entire physical server and is not shared by anyone else. Unlike VPS and Shared hosting the user has full control over the server. The user can choose the hardware, software, OS, etc. Dedicated server is useful because of the benefits like high performance, security, email stability and control. This option is the costliest as you are the only one who is bearing the cost of the entire server. Most of the providers offer Managed dedicated server where the server is managed by the provider upto some extent.
Dedicated server is recommended for big companies and institutions who have huge data and perform multiple tasks and calculations. Dedicated server is expensive but you have full control over the server and you can install anything you require for your site. With a dedicated server you have ample resources to handle any volume of requests for your site.