Citrix Receiver is an essential part for users to receive desktops and applications from XenDesktop because it is the other end of the connection. Remember when you were a kid and you would take two tin cans and put a piece of long string between them to talk to your friend at the other end? Think of XenDesktop as one side (server), Receiver as the other side (client), and the ICA/HDX protocol as the string in between them. Receiver is a critical component in the communication link between the client and the server. This setup is illustrated in the following figure:

Citrix Receiver allows the virtual desktop to run on the client device. Technically, Citrix Receiver just displays the screen pixels on the client device, while the actual virtual desktop is running back in the data center on a server. The simplest way to describe the Receiver to ICA to XenDesktop connection is that Receiver is just a display device with a very long Keyboard, Video, and Mouse (KVM) cable...