A reference frame is a set of coordinates or a viewpoint used to measure and describe the position and motion of objects. It provides a context for understanding how an object moves relative to other objects. For example, in physics, a stationary reference frame might be the ground, while a moving reference frame could be a car traveling down a road. Different reference frames can lead to different observations of the same event. For instance, an observer on the ground may see a train moving quickly, while a passenger inside the train perceives themselves as stationary. This concept is crucial in fields like physics and astronomy.