mobility (n.)

early 15c., "capacity for motion, ability to move or be moved, property of being easily movable," from Old French mobilité "changeableness, inconsistency, fickleness" and directly from Latin mobilitatem (nominative mobilitas) "activity, speed," figuratively "changeableness, fickleness, inconstancy," from mobilis "movable, easy to move" (see mobile (adj.)). Socio-economics sense of "possibility of movement between different social levels" is from 1900 in sociology writing.