Backend is the "inner part" of a website that runs on the server. It processes user requests, interacts with databases, and handles business logic.
Backend developers use programming languages like Python, PHP, Java, C# (.NET), Node.js and others. They also use frameworks such as Django, Spring, ASP.NET, Express.js.
The main task of backend development is to ensure reliable website operation, data storage, and communication between users and the server.