A simple client program or hardware device which relies on most of the function of the system being in the server.
Gopher clients, for example, are very thin; they are stateless and are not required to know how to interpret and display objects much more complex than menus and plain text. Gopher servers, on the other hand, can search databases and provide gateways to other services.
By the mid-1990s, the model of decentralised computing where each user has his own full-featured and independent microcomputer, seemed to have displaced a centralised model in which multiple users use thin clients (e.g. dumb terminals) to work on a shared minicomputer or mainframe server. Networked personal computers typically operate as "fat clients", often providing everything except some file storage and printing locally.
By 1996, reintroduction of thin clients is being proposed, especially for LAN-type environments (see the cycle of reincarnation). The main expected benefit of this is ease of maintenance: with fat clients, especially those suffering from the poor networking support of Microsoft operating systems, installing a new application for everyone is likely to mean having to physically go to every user's workstation to install the application, or having to modify client-side configuration options; whereas with thin clients the maintenance tasks are centralised on the server and so need only be done once.
Also, by virtue of their simplicity, thin clients generally have fewer hardware demands, and are less open to being screwed up by ambitious lusers.
Never one to miss a bandwagon, Microsoft bought up Insignia Solutions, Inc.'s "NTRIGUE" Windows remote-access product and combined it with Windows NT version 4 to allow thin clients (either hardware or software) to communicate with applications running under on a server machine under Windows Terminal Server in the same way as X had done for Unix decades before.