The notation "f'(x)" represents the derivative of a function f at a specific point x. The derivative measures how the function's output changes as the input changes, essentially indicating the function's rate of change or slope at that point. In practical terms, if you have a graph of f, the derivative at x tells you how steep the graph is at that location. A positive derivative means the function is increasing, while a negative derivative indicates it is decreasing. The derivative is a fundamental concept in calculus, used in various fields such as physics, engineering, and economics.