What defines mid-fi versus high-end?

'Mid-Fi' is an arbitrary marketing term thrown about loosely by those with something to gain by creating artificial barriers to entry. And painting products, even entire brands with that brush, they hope to justify there own products and brands exorbitant pricing. Case in point is Marantz. Their products span pricing from $500 to $10,000. A $500 receiver is of necessity a cost engineered product; a $9,000 integrated  amp, decidedly less so, and clearly a 'high-end' product. Yet despite impeccable technical execution, I have heard it derided as 'too mid-fi'. That is simple snobbery with some unacceptable implied overtones.

Does it matter what you or others call it? If you are entertained by and enjoy it...

The key is to get the best sound reproduction for YOU within your budget.

Answer: your income.  What you can afford is seen inevitably as the "low-end" of audiophilia.  The highest end is always to dream for, whether $5,000 or $500,000.  Does really high quality sound demand that?  No, not at all.  But human nature does.

I thought I was omniscient, but frankly, this one has me stumped. 

There are different levels if HI-FI.  I guess it is difficult question. Everyone's ears are different, tastes are different. I would define HI Fi as being pure sounding music with a full bodied spectrum of sound and dynamics. Not a bose wave radio though they sound good.  After you reach a certain dollar level you have to pay out much more $$$$$$$ to reach the next level. You get to the point where for me I get very happy and do not need to upgrade for a few decades. Spending money on HI Fi is not a hobby for me. Enjoying a great sounding system is a joy in life and a blessing.