Thinwire is one of the cornerstone components in the Citrix HDX technology set (whay used to be called SpeedScreen and such).The following video gives you a quick introduction on Thinwire and its role in the HDX technology stack.

Thinwire is responsible for remoting 2D graphics across the network efficiently to provide a rich user experience. This component has been part of XenApp for many years. Many of the HDX technologies like image acceleration, progressive display, queuing and tossing and super cache are built on top of the Thinwire Virtual Display Adapter.

Source: http://community.citrix.com/blogs/citrite/juanr/2009/08/06/HDX+Learning+Series+-+Thinwire+Virtual+Display+Adapter