In software development, the back-end refers to the part of an application that handles data storage, processing, and management. This includes the server, database, and application logic that powers the application's functionality, but is not directly visible to the end-user. The back-end interacts with the front-end, which is the part of the application that users see and interact with. In a web application, for example, the back-end might handle user authentication, process and store data from user input, and generate dynamic content to be displayed on the front-end. Back-end development requires a solid understanding of programming languages, data structures, and algorithms, and is essential for building scalable, secure, and robust software applications.