The middle class is something in between the capitalist class and the working class, it's badly defined.

If you're in the capital class, you're getting your income from the assets you own. If you're in the working class, you're getting your income from working.

I've heard multiple definitions for a middle class, eiher one that owns some capital in the form of rental apartments or stocks, or that the middle class has a decenr amount of discretionary income.

Personally I don't think the middle class is that useful of a term to make sense of the economy. I also have a feeling that people like the term middle class because it muddies the waters when it comes to understanding the relationship between capital and labor.