A dedicated server is a type of Internet hosting where the client leases an entire server not shared with anyone.
This is more flexible hosting as organizations have full control over the server(s) and they can choose their operating systems, hardware, etc...
Dedicated servers are most often housed in data centers. A company who lease out these servers is called dedicated hosting provider.
Hosting company provides managed & unmanaged type of dedicated server. Many dedicated hosting provider also offers choice of operating system and advanced control panles.
You've total control over the RAM, Hardware, Firewall and many other components of your dedicated server.