A non-inertial frame is a reference frame that is accelerating or rotating, meaning it is not at rest or moving at a constant velocity. In such frames, observers may experience fictitious forces, like the Coriolis force or centrifugal force, which appear due to the acceleration of the frame itself. For example, when a car makes a sharp turn, passengers feel pushed against the door, even though no real force is acting on them. In contrast to inertial frames, where Newton's laws of motion hold true without modification, non-inertial frames require adjustments to these laws. This is because the effects of acceleration must be accounted for to accurately describe motion. Understanding non-inertial frames is essential in fields like physics and engineering, where analyzing forces in accelerating systems is crucial.