In non-relativistic mechanics (including quantum mechanics, actually, but here I'll be talking about classical non-relativistic mechanics) basically everything is relative. You have a (sort of)) privileged class of reference frames (as is true in special relativity) called inertial reference frames, and the inability to detect any absolute motion (put simply). Given two individuals (say you and me) who both believe themselves to be at rest (because we aren't accelerating), yet are in relative motion with respect to one another, it is impossible for either individual (or for anybody else) to say that one of these is actually the individual in motion.
Relative velocities, relative positions, etc., are all aspects of Galilean relativity that governs the symmetries of non-relativistic classical mechanics.
In special relativity, we actually have things turn out less "relative" because we have one reference frame (that of light) which is in a sense absolute and which provides the fundamental invariants and symmetries for relativistic mechanics. Regardless of whether you think you are at rest and I am in motion or vice versa, we can both measure the same speed for light. That's not relative, it's invariant.
That's not how relativity works (Galilean or special or general relativity), nor does it make any real sense at all.
