When working with Terminal Servers, the term "RDP" will come up frequently. As mentioned previously, RDP is a protocol that runs on TCP/IP (much like SMTP, HTTP, etc.). However, you'll also see the term "RDP" used as a file type. RDP files have the extension .RDP, just as Word documents have .DOC extensions.
The RDP Protocol
The Remote Desktop Protocol (RDP) is the network protocol used by Terminal Service client devices for client-to-server session communication. The RDP protocol actually transmits keystrokes and mouse movements from the client to the server, and screen images from the server to the client. This protocol is also responsible for connecting client resources, such as mapping a user's clipboard, local drives, and local ports, as well as printing and encryption.
The RDP protocol is a high-level TCP/IP protocol that can run over port 3389 (although you can change this port). It is the only server-based computing protocol that Terminal Server supports out of the box, although various third-party products use their own protocols rather than RDP.
RDP files contain information that RDC clients use to connect to Terminal Servers. A user can simply double-click an RDP file to launch their RDC client and establish a session with the server specified in the RDP file. These files also contain settings and configuration information for the session, including screen resolution, color depth, and device options.