A web application is a site with interactive elements. They allow users to interact: click buttons, fill out forms, ask for a price, and make purchases. Email clients, social networks, search engines, online stores, and project management programs are all examples of such applications. In terms of architecture, web applications consist of two parts: client and server. The client side is also called the interface. In essence, this is what users see on the screen of the device. The server part, or back-end, is the software and hardware part of the service. This is a set of tools that implement the application logic.