The programming concept that involves writing code that can be reused in different projects is called modularity. By breaking down code into functions, classes, or modules, developers can create organized, maintainable, and scalable codebases. This approach enhances collaboration and speeds up development, as routines can be applied across various applications. Utilizing modular design also improves debugging, allowing developers to isolate issues more effectively. Overall, modularity is essential for creating efficient and robust software solutions.