What was behind the web interface? What was the backend?

The web front-end usually consists of a frontend application that interacts with the user through a browser. Depending on the project, this could be a SPA (Single Page Application) built with React, Vue, or Angular, or a traditional server-rendered application.

The backend is typically implemented using one of the popular server-side languages and frameworks: Node.js with Express, Python with Django/Flask, Java with Spring, or .NET. It handles business logic, database interactions, and APIs for the frontend.

For example, in a typical project, the React frontend communicates with a REST API on Node.js, which interacts with a PostgreSQL database.