A decreasing function is a type of mathematical function where, as the input value increases, the output value decreases. This means that for any two points on the function, if the first point has a larger input than the second, the output of the first point will be less than the output of the second. Graphically, decreasing functions slope downwards from left to right. An example of a decreasing function is the linear function represented by the equation f(x) = -2x + 3. In this case, as the value of x increases, the value of f(x) decreases. Decreasing functions are important in various fields, including economics and physics, where they can represent scenarios like diminishing returns or loss of energy.