The correct answer is C) Deviation is the angle between the magnetic meridian and the axis of the compass card. Deviation is the difference between the direction indicated by the compass and the true north direction. This difference is caused by the influence of magnetic materials on the ship, which can distort the earth's magnetic field and cause the compass to point in a slightly different direction. The angle between the magnetic meridian (the direction of the earth's magnetic field) and the axis of the compass card is known as the deviation. The other options are incorrect because they do not accurately describe the definition of deviation. Option A refers to the degaussing meridian, which is not the same as the magnetic meridian. Option B describes the angle between the true meridian and the magnetic meridian, which is known as variation, not deviation. Option D refers to the angle between the true meridian and the axis of the compass card, which is not the definition of deviation.