XenApp and XenDesktop can be used in isolation or combined to allow the separation of applications from the desktop, which reduces the overall number of virtual desktop images that need to be managed.
With XenApp you can place a single copy of an application on a centralised XenApp server, rather than having multiple copies of the application running on desktops. In addition to increasing application and network performance, hosting an application on a XenApp server greatly simplifies Windows application delivery. For example, it is much easier to patch just one copy of an application running on a XenApp server, rather than patch multiple copies of an application running on desktops.
XenDesktop is a desktop virtualisation system that is used to centralise and deliver Microsoft Windows 7, Vista or XP virtual desktops as a service to users anywhere on any device. Virtual desktops are dynamically assembled from a pool of server resource, on demand, providing users with personalised, desktops each time they log on. The open architecture of XenDesktop offers choice and flexibility of virtualisation platform and endpoints. It simplifies desktop management by using a single image to deliver personalised desktops to users and enables administrators to manage service levels with built-in desktop performance monitoring.