Viewdata is a technology that allows users to access information from remote sources through a computer network. There are several synonyms for viewdata, including videotex, teletext, and prestel. Videotex refers to the technology of providing interactive information services between a user and a computer network, while teletext is a broadcast system that provides information and news on TV screens. Prestel, on the other hand, is a commercial online service that enables users to access a wide range of information and services through their television sets. In general, all these terms refer to technologies that provide a way for users to access information across a network, but they differ in their specific characteristics and applications.