The power rule is a calculus rule used to find the derivative of a function that is raised to a constant power. It states that if f(x) = x^n, where n is a constant, then the derivative of f(x) with respect to x is equal to n*x^(n-1).
The rate at which a function changes as its input variable changes. It represents the slope of the tangent line to the graph of a function at any given point.