body axis
noun
1Each of a set of geometrical axes which define directions with respect to a three-dimensional object; (Aeronautics ) each of a set of rectangular coordinate axes having their origin at the centre of gravity of an aircraft and the x-axis along its longest dimension.
2 Biology a main line of growth, direction, organization, or symmetry within the body of an organism.
Origin
Mid 19th century; earliest use found in Transactions of the American Philosophical Society.