three-tier client/server (thrē`tēr klī`ənt-sərvər) noun

An client/server architecture in which software systems are structured into three tiers or layers. The three layers are called user interface, business logic, and database. Layers may have one or more components. For example, there can be one or more user interfaces in the top tier, each user interface may communicate with more than one application in the middle tier at the same time, and the applications in the middle tier may use more than one database at a time. Components in a tier may run on a computer that is separate from the other tiers, communicating with the other components over a computer network. See also client/server architecture. Compare two-tier client/server.