Virtual Desktop Infrastructure (VDI) is a technology that allows desktops to live virtually on shared infrastructure like a server farm or in the cloud. Software and/or small hardware clients can be used by end-users to connect to their desktop environment ad-hoc. VDIs can be used for their flexibility, easier management of desktop operating systems (e.g. security updates) and as a cost-savings measure. The option mentioning VMWare and VirtualBox is close but it specifically states servers not desktops which makes it incorrect.
Desktop virtualization is a software technology that separates the desktop environment and associated application software from the physical client device that is used to access it.
Desktop virtualization can be used in conjunction with application virtualization and user profile management systems, now termed user virtualization, to provide a comprehensive desktop environment management system. In this mode, all the components of the desktop are virtualized, which allows for a highly flexible and much more secure desktop delivery model. In addition, this approach supports a more complete desktop disaster recovery strategy as all components are essentially saved in the data center and backed up through traditional redundant maintenance systems. If a user's device or hardware is lost, the restore is straightforward and simple, because the components will be present at login from another device. In addition, because no data are saved to the user's device, if that device is lost, there is much less chance that any critical data can be retrieved and compromised.