Final answer:
The rate of change of displacement is defined as velocity, a vector quantity measured in units like meters per second or kilometers per hour.
Step-by-step explanation:
The physical quantity that is defined as the rate of change of displacement is known as velocity. Displacement is a vector quantity, which means it has both magnitude and direction. The SI unit for displacement is the meter. Velocity also considers the direction of an object's motion and is typically measured in units such as meters per second (m/s) or kilometers per hour (km/h). Velocity is a fundamental concept in kinematics, the study of motion, and is crucial for understanding how objects move in space.