RDP stands short for Remote Desktop Protocol. This protocol allows certain types of communication between the user (or the client) and the server.
The exchange goes in the way that the user gives out keystrokes and mouse clicks and in return the server provides images and pictures as requested from the user. RDP is the only protocol that is server-based that a terminal server can support out of the PC box. Of course, there is a variety of other protocols used but RDP is the most common one.
To be even simpler, a remote desktop protocol allows one user to connect to a virtual network server and expose graphic interface to another remote desktop.
While doing this, it is important to note that the same protocol must be used by both of the computers connected to a server on the network.
That Is how creating a virtual network is made possible and communication can be made. RDP can support allot of channels and also allows encryption of the data.