MK II & MK III

I tried this question on another forum & no luck.  Maybe someone here knows.  This may be a dumb question.  What’s with all the mk II & mk III stuff.  I see it on various brands & an equally varied type of things.  Turntables, my new phono preamp & cartridges.  I’m pretty sure I saw an amp & some speakers Both for sale here. 

I’ve googled & did a thread search here. I can’t find anything that explains with at it is or makes something an “mk” let alone a II or III.

Unless... My Kryptonite?? Some of the stuff I see makes me weak in the knees, my head spins & I drool profusely.  There’s also a Lincoln MK II but, I’m just throwing that in for fun.

I’m really curious.  Thanks for sharing your knowledge.