A virtual appliance is a virtual machine image file consisting of a pre-configured operating system environment and a single application. The purpose of a virtual appliance is to simplify delivery and operation of an application. To this end, only necessary operating system components are included.
A virtual machine (VM) is a software computer that, like a physical computer, runs an operating system and applications.
A virtual storage appliance (VSA) is a storage controller that runs on a virtual machine(VM) to create shared storage without the cost of additional hardware.