Back-end development refers to the server-side aspect of web or software development, focusing on what happens behind the scenes when a user interacts with a website or application. This area of development deals with the server, database, and application logic, ensuring that data flows smoothly between the front-end (the part the user interacts with) and the back-end. Back-end developers work with programming languages like Java, Python, Ruby, and PHP, and use frameworks like Node.js, Django, or Ruby on Rails to build robust and scalable systems.

In back-end development, managing and organizing data is crucial. Developers often work with databases (such as MySQL, PostgreSQL, or MongoDB) to store and retrieve information, and they create APIs (Application Programming Interfaces) that allow the front-end and other services to communicate with the server. Security, performance, and scalability are key considerations, as back-end systems must handle large volumes of data and requests efficiently and securely, especially in applications that serve a large number of users.