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A thin client, sometimes called a lean client, is a a low-cost endpoint computing device that relies heavily on a server for its computational role. The term thin client is also used to describe software applications that use the client-server model in which the server performs all the processing. Thin clients and other lean devices rely on a network connection to a central server for full computing and don't do much processing on the hardware itself.
The term is derived from the fact that small computers in networks tend to be clients and not servers and the idea that since the goal is to limit the capabilities of thin clients to only essential applications, the devices tend to be purchased and remain "thin" in terms of the client applications they include. In general, thin clients are centrally managed, are not as vulnerable to malware attacks, have a longer life cycle, use less power and are less expensive to purchase. Since the idea is to limit the capabilities of thin clients to only essential applications, they tend to be purchased and remain "thin" in terms of the client applications they include.
Thin clients can be contrasted with thick or fat clients, which are essentially desktop PCs that can handle all the functionality of a server if required. A very thin client may be referred to as a zero client. A typical zero client product is a small box that serves to connect a keyboard, mouse, monitor and Ethernet connection to a remote server. The server, which hosts the client's operating system (OS) and software applications, can be accessed wirelessly or with cable. Zero clients are often used in a virtual desktop infrastructure (VDI) environment.