Low Fi / Mid Fi / High Fi ?

Guys I would like to know what the imaginary guidelines are! It can't be price.Since there's alot of great gear that doesn't make you mortgage the house!And this Hifi sound thing...some refer to hifi as bad...what gives?LowFi is easy for me ,just about any audio component out of a big chain store(mass market).In a blindfold test does anyone think they would be able to tell the difference between this midfi or hifi thing? Or do we use this as a tool to feel better about spending so much money on this stuff.Is there a mystical book that puts these components in catergories?Please fellow audiophiles fill me and others in on this.

Thanks in advance!