N-tier or multitier architecture is a way of organizing and dividing the components of a computer system into distinct layers or tiers. The tiers can be defined based on the functionality of the components or the computing environment in which the system will run. When the tiers are based on the functionality of the components, the architecture is considered a control and communication pattern. However, when the tiers are defined with an eye toward the computing environment, the architecture is considered an allocation pattern.
Tiers refer to physical partitions and are also associated with multilayered architecture. The three-tier design, which divides logic into the display, business, and data layers, is one of the most extensively used forms of layered architecture.