Back-end is the part of a website (or application ) which is not accessible to the user. The back-end part runs on the server and is responsible for data storing and application logic which makes back-end necessary for the proper functioning of the front-end part of a website (or application).
The back-end developer is responsible for building this part of an application which runs on the server and is not accessible to the user.
The back-end developer needs to build an application and make all the back-end parts communicate with each other.
The most popular back-end programming languages are Python, Java, C# and PHP. In order to create secure and scalable applications, back-end developers should also be familiar with architectural patterns (SOA, CQrs, serverless), databases and security issues (CORS, SSL/TLS, HTTPS).
If you like to solve business problems, create services, write algorithms and solve performance issues then probably the back-end is a path for you.
The full back-end roadmap showing you step by step how to become a modern back-end developer is available Click Here