mk II or mk III?

Im relatively new so, this may be a dumb question.  What gives with al the mk II & mk III stuff.  I see it 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 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.

I’m really curious.  Thanks for sharing your knowledge.
You will also see V2 for "version 2" sometimes used, it means the same thing. 
It usually connotes an upgrade. MK-I, MK-2, MK-3.  For example, my current cartridge is an AudioTecnica MK-III.  Also used by some manufacturers is a "Special Edition" designation which marks an improvement. For example, Audio Research uses the "special edition" designation with the logo "SE."

Small manufacturers are always finding little improvements to the products they offer. Often they will incorporate groups of them and call the upgraded unit a mk 2, or mk3. They want to keep the word of mouth and review promotional value gained by the original product instead of calling it a new name!                      
Some companies do this a lot more than others.