A computer architecture that adds a middle layer, called the application server, to the two-tier client-server model. In a three-tier model, the client, or front end, contains the user interface, while the backend, or resource manager, is usually a database. The middle layer, or application server, handles the application logic, providing services to the client and interacting with the resource manager as needed. Communication among the three layers is managed by middleware. Three-tier architecture allows for the greatest flexibility in distributing clients and servers across multiple platforms and machines.
A type of network that contains three layers: workstations that run a user interface, a middle layer that runs applications, and a database management layer that stores data needed by the application layer.