Citrix XenApp is an application virtualization service that provides on-demand Windows-based applications to devices and works in the context of the Citrix XenDesktop desktop virtualization service.
Techopedia explains Citrix XenApp
Citrix XenApp provides features such as user self-storage, mobile touchscreen optimization and various user experience enhancements. The developer, Citrix Systems, maintains that this tool can decrease transaction times for client/server operations by up to 300%, while supporting strategies like "bring your own device" by serving a distributed network with remote access and agile design. Delivering what Citrix calls "virtual app access," Citrix XenApp is part of a concerted strategy to create services that make the most of new technologies like cloud computing, software as a service and networking hardware virtualization.