A virtual private server (VPS) is a virtual machine sold as a service by an Internet hosting service. A VPS runs its own copy of an operating system & customers have superuser-level access to that operating system instance, so can install almost any software that runs on that OS. For many purposes they are functionally equivalent to a dedicated physical server, and being software defined are able to be much more easily created and configured.
With unmanaged hosting, the customer is left to administrate their own server instance.
Unmetered hosting is generally offered with no limit on the amount of data-transferred on a fixed bandwidth line. Usually, unmetered hosting is offered with 10 Mbit/s, 100 Mbit/s or 1000 Mbit/s (with some as high as 10Gbit/s). This means that the customer is theoretically able to use 3.33~ TB on 10 Mbit/s, 33~ TB on 100 Mbit/s and 333~ TB on a 1000 Mbit/s line per month (although in practice the values will be significantly less). In a virtual private server, this will be shared bandwidth and (should) mean there is a fair usage policy involved. Unlimited hosting is also commonly marketed but generally limited by acceptable usage policies and terms of service. Offers of unlimited disk space and bandwidth are generally false due to carrier capacities and technological boundaries.
Main article: Cloud computing
A VPS which is dynamic (that is, it can be changed at runtime) is often referred to as a cloud server. Key attributes for this are:
Additional hardware resources can be added at runtime (CPU, RAM)
Server can be moved to other hardware while the server is running (automatically according to load in some cases)
Also referred to as Virtual Dedicated Server