A programming function is a reusable block of code designed to perform a specific task. It takes input, called parameters, processes it, and often returns an output. Functions help organize code, making it easier to read, maintain, and debug. They can be defined in various programming languages, such as Python, Java, or JavaScript. Functions can be built-in or user-defined. Built-in functions are provided by the programming language, while user-defined functions are created by programmers to meet specific needs. By using functions, developers can avoid repetition and enhance code efficiency, leading to better software development practices.