MidFi is just code for the lower end of HiFi. Hardly anyone uses it any more since it came to be regarded as a sort of mild put down when all it really means is budget. But everyone is on a budget, just different amounts, so it never really made any sense no matter how you look at it.
If you read a book like Robert Harley's The Complete Guide to High End Audio (highly recommended) you will learn that what really differentiates the High End from other home electronics is nothing to do with price or exclusivity or anything like that. The key to being High End is the whole focus of High End audio is sound quality. Not features, not looks, sound quality. Making music sound so good you want to stop everything and sit down and enjoy just listening to the music.
This is High End audio. Yes there definitely are huge differences in sound quality and yes the very best does cost more. But that doesn't mean you can't build a really impressively satisfying music system on a modest budget. I have done it. Lots of us have. I wouldn't think to call the $1200 systems I made mid-fi.
To be honest, the term HiFi isn't always all that complimentary. There are people who like the HiFi sound, and they will spend a fortune on their Mark Levinson, Wilson, etc and maybe even be happy. That should never stop you from thoroughly enjoying whatever it is you thoroughly enjoy, whether someone calls it LoFi, MidFi, HiFi, or NoFi.
So if you hear those terms just take it as this is their way of telling you how good they think it is relative to other stuff. This is all relative anyway so don't try and read too much into it.
