**Definition:**
A function is a block of code in programming that performs a specific task and can be reused throughout a program. It takes inputs, called parameters, and produces an output.

**Key ideas:**
- Functions help organize code into manageable sections.
- They can be called multiple times, reducing repetition.
- Functions can return values, which can be used later in the program.
- They improve code readability and maintainability.

**Why this topic matters in this category:**
Understanding functions is essential in computer programming, as they are fundamental building blocks for creating efficient and effective software.