What is the definition of Mobility?

Mobility: the ability to move or be moved freely and easily.

Release techniques, joint mobilizations, stretching and instrument assisted soft tissue mobilizations are all techniques designed to increase mobility, usually measured as the range of motion allowed at a joint. See also: hypermobility and hypomobility

Origin - early 15c., "capacity for motion," from Old French mobilité "changeableness, inconsistency, fickleness," from Latin mobilitatem (nominative mobilitas) "activity, speed," figuratively "changeableness, fickleness, inconstancy" (Etymology Online)