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 feeling of being pushed back in a car that suddenly accelerates. These forces are not due to any physical interaction but arise from the acceleration of the frame itself. In a non-inertial frame, the laws of physics appear different compared to an inertial frame, where objects follow Newton's laws without any additional forces. For example, in a rotating frame, an object may seem to be pushed outward due to the centrifugal force, which is a result of the frame's rotation rather than an actual force acting on the object.