What does "deviation" mean?

Additional senses

1. 2.(Com.) The voluntary and unnecessary departure of a ship from, or delay in, the regular and usual course of the specific voyage insured, thus releasing the underwriters from their responsibility. Deviation of a falling body (Physics), that deviation from a strictly vertical line of descent which occurs in a body falling freely, in consequence of the rotation of the earth. -- Deviation of the compass, the angle which the needle of a ship's compass makes with the magnetic meridian by reason of the magnetism of the iron parts of the ship. -- Deviation of the line of the vertical, the difference between the actual direction of a plumb line and the direction it would have if the earth were a perfect ellipsoid and homogeneous, -- caused by the attraction of a mountain, or irregularities in the earth's density.