Citrix Server and Terminal Services

I was quite familiar with Terminal Services in Windows and also the Remote Desktop Protocol used in it. But recently I came across a technology called 'Citrix' that was similar in nature, so I decided to dig into the root of it. This is the info I found on the net:

Citrix Presentation ServerSoftware from Citrix that provides a timeshared, multiuser environment for Unix and Windows servers. Formerly MetaFrame, Citrix Presentation Server uses the ICA protocol to turn the client machine into a terminal and governs the input/output between the client and server. Applications can also be run from a Web browser
Citrix Presentation Server (formerly Citrix MetaFrame) is a remote access/application publishing product built on the Independent Computing Architecture (ICA), Citrix Systems' thin client protocol. The Microsoft Remote Desktop Protocol, part of Microsoft's Terminal Services, is based on Citrix technology and was licensed from Citrix in 1997. Unlike traditional framebuffered protocols like VNC, ICA transmits high-level window display information, much like the X11 protocol, as opposed to purely graphical information.

Independent Computing Architecture (ICA) is a proprietary protocol for an application server system, designed by Citrix Systems. The protocol lays down a specification for passing data between server and clients, but is not bound to any one platform.
Practical products conforming to ICA are Citrix's WinFrame and MetaFrame products. These permit ordinary Windows applications to be run on a suitable Windows server, and for any supported client to gain access to those applications. The client platforms need not run Windows, there are clients for Mac and Unix for example.