The expression e^-x represents an exponential function where e is the base of natural logarithms, approximately equal to 2.71828. The negative exponent indicates that the function decreases as x increases. This means that as you move to the right on a graph, the value of e^-x approaches zero but never actually reaches it. This function is commonly used in various fields, including mathematics, physics, and finance. It models processes such as decay and growth, where the rate of change is proportional to the current value. For example, it can describe how a substance decays over time or how populations grow under certain conditions.