A thin client, sometimes called a lean client, is a low-cost, centrally-managed computer devoid of CD-ROM players, diskette drives, and expansion slots. The term derives from the fact that small computers in networks tend to be clients and not servers. Since the idea is to limit the capabilities of these computers to only essential applications, they tend to be purchased and remain "thin" in terms of the client applications they include. As software as a service (SaaS) gains popularity, it is expected that thin clients and blade PCs will replace desktop PCs in many work and educational environments. In general, they are not as vulnerable to malware attacks, have a longer life cycle, use less power and are less expensive to purchase.
Thin client is also used to describe software applications that use the client-server model where the server performs all the processing.
See also: fat client.