In computer architecture and software design, the “middle tier” is a layer of software that sits between the user interface and the back-end database or other data storage and management systems.
The middle tier is responsible for processing and managing data, as well as providing application logic and business rules to the user interface. It acts as a mediator between the presentation layer (i.e., the user interface) and the data storage layer, enabling the two layers to interact with each other.
Typically, the middle tier is made up of one or more application servers or web servers, and is responsible for handling user requests, processing and transforming data, enforcing security policies, and caching data to improve performance.
In a three-tier architecture, the three layers are typically the user interface (front-end), the middle tier (application logic), and the data storage layer (back-end).