With the use of virtualization software, physical servers can be partitioned into multiple 'virtual' servers where each virtual server looks and acts like an individual dedicated server. Virtual Servers can run their own operating systems which means that each system can be administered independently - including system re-boot.
A Virtual Private Server (VPS) is one instance of a Virtual Server. It has its own operating system, applications and data which are all isolated from all other data that resides on the physical server. A Virtual Private Server can enable you to leverage the benefits of dedicated servers at a fraction of the cost.