A function is a mathematical concept that describes a relationship between two sets of values. It takes an input, often called an argument, and produces a single output based on a specific rule. For example, in the function f(x) = x + 2, if you input 3, the output will be 5. Functions can be represented in various forms, including equations, graphs, and tables. Functions are essential in many fields, including science, engineering, and economics. They help model real-world situations, allowing us to predict outcomes and analyze data. Understanding functions is crucial for solving problems and making informed decisions based on quantitative information.