Definition - What does X Client mean?
X client refers to the application program that is displayed on an X server, although this application program is otherwise separate from that server. All application programs that run in a GUI delivered by the X Window Sytem, which is virtually any GUI employed on Linux as well as other Unix-like operating systems, is considered an X client. Therefore Apache, OpenOffice, gFTP, gedit, GIMP, Xpdf, and rCalc are typically X clients if employed on such operating systems.
Techopedia explains X Client
An X server refers to an application program in the X Window System that is operated on local machines. X server manages every access to the display screens, graphics cards and input devices (such as a mouse or keyboard) on those computers for the GUIs. The X Window System, also known as simply X, is a comprehensive, free client-server system used to manage GUIs on individual computers as well as on computer networks.
In the standard client-server architecture, the client program is implemented on the local system and the server program is implemented either on the local system or on the remote system, that is, any other system in the computer network. However, in the X Window System, this architecture is reversed, where every local system implements the X server program and accesses the X client applications operating either on the exact same system or on another remote system. As a result, there is no need for the application programs to be aware of the specifications of monitors, graphics cards, and other installed hardware. This simplifies the creation of such programs and facilitates their services to several users on the network concurrently.
One of the major features of the X Window System is its network transparency. This signifies that virtually any X client may operate either on the local system or on the remote system without exhibiting any evident impact on the users in most instances. This provides numerous important benefits, such as greater intuitiveness for common users and simplified management.