VMware describes Virtual Desktop Infrastructure (VDI) as “delivering desktops from the data center”. In other words, VDI is where enterprise desktop computers are virtualized, moved to the data center, then presented over the LAN or WAN to the end users. Once VDI is used, typically the end user devices are replaced with thin-client devices.
While VMware has a VDI product called VDM (Virtual Desktop Manager), VDI is not a product exclusive to VMware. Other VDI vendors include Citrix XenDesktop & Kidaro (now owned by Microsoft).
With VDI, virtual desktops are served by enterprise virtualization servers running products like VMware ESX, Microsoft Hyper-V, and Xen Server. With the addition of the VDI products, these desktops can be dynamically created, pooled & shared, or even accessed from a GUI menu, over a web page.
The graphic below, shows some examples of how VDI could be used and how it works.
Figure 1: Image Source: VMware.com