A subroutine is a set of instructions designed to perform a specific task within a larger program. It allows programmers to break down complex problems into smaller, manageable parts, making the code easier to read, maintain, and reuse. Subroutines can take inputs, process them, and return outputs, which helps streamline the overall functionality of the program. In many programming languages, subroutines are also known as functions or methods. They can be called multiple times throughout a program, reducing redundancy and improving efficiency. By using subroutines, developers can create modular code that enhances collaboration and simplifies debugging.