an applications program that communicates with the server, sending it requests such as "draw a line" or "pay attention to keyboard input
an application that draws graphics to a screen in the X environment, and gets input from the devices attached to that screen
an application that wants to display a window on the server, like a web browser or email application
a program that interfaces with an X server (almost always via the X libraries), and thus with some input and output hardware like a graphics card, monitor, keyboard, and pointing device (such as a mouse)
a program that runs either on your computer or a remote computer, and communicates with an X server for display, input, and output
a program that uses the X libraries to interface with an X server, and thus with some input and output hardware like a graphics card, monitor, keyboard, and pointing device (such as a mouse)
An applications program that communicates with an X server to request that it display information on a screen or to receive input events from the keyboard or a pointing device such as a mouse. The client may be running on the same computer as the server (local), or it may be connected via a network (remote).
An application or tool that displays on an X server. X clients can also called X applications.