The first derivative of a function measures how the function's output value changes as its input value changes. In simpler terms, it tells us the rate of change or the slope of the function at any given point. If you think of a graph, the first derivative indicates whether the graph is rising, falling, or flat at that point. In calculus, the first derivative is often denoted as f'(x) or dy/dx. It is a fundamental concept used in various fields, including physics, economics, and engineering, to analyze trends and optimize functions. Understanding the first derivative helps in determining maximum and minimum values of functions.