the quality or state of being relative
the state of being dependent for existence on, or determined in nature, value, or quality by, a relation to something else
a theory based on the postulates that the speed of light in a vacuum is constant and independent of the source or observer and that the laws of physics are the same in all systems, leading to the assertion that mass, dimension, and time will change with increased velocity
a theory which is based on the two postulates (one) that the speed of light in a vacuum is constant and independent of the source or observer and (two) that the laws of physics, as expressed mathematically, are the same in all systems, leading to the assertion that mass and energy are equivalent and that mass, dimension, and time will change with increased velocity
an extension of this theory to include gravitation and related acceleration phenomena