The backend side of a system is one or more applications running on machines that are commonly referred to as servers. The purpose of these applications is to serve requests coming from other applications—clients—and execute the necessary steps to accomplish the given request (validate the input, verify the requester's permissions, query and update rows in the database, run algorithms and workflows, and, at the end, return a response that the client side can then use to determine how to proceed.     

The backend side of a project is like the soil in a flower field—if the soil is healthy, it enables a flourishing field with lovely flowers. However, if the soil is dry and not taken care of, the flowers will die and the field will cease to exist.

In our case, the field is the backend server and the flowers are our users—the backend needs to be reliable, secure, fast, and scalable in order to support many happy users and to create a successful product.

The world of backend development is extensive — there are a vast amount of programming languages and technologies that you can choose from. Each of them looks at this world from a slightly different angle, enabling different targets. For example, C# is a very powerful language that comes with plenty of handy tools, JavaScript allows you to write the backend and the frontend using the same programming language, and Python is suitable for systems based on math and complex algorithms.

Fortunately, whatever the technology of choice is, its interface to external systems will follow the same protocols as other backend systems — HTTP and JSON, which allow the creation of RESTful APIs. This enables strict separation of concerns between the backend and the frontend — each of them can be created using a different set of technologies but they will still be able to communicate flawlessly.