Instantaneous speed refers to the speed of an object at a specific moment in time. It is different from average speed, which measures the total distance traveled over a total time period. Instantaneous speed can be determined using a speedometer in a car or by analyzing a graph of an object's motion. To calculate instantaneous speed mathematically, one can use the derivative of the position function with respect to time. This concept is essential in physics and helps in understanding how fast an object is moving at any given instant, providing valuable information in various applications, such as automotive engineering and sports science.