Class is a social and economic relationship within the economy based on property ownership. Class has less to do with how much money someone makes and more to do with how much ownership they have over their labor.
Someone who must work for a living and has no control over their job is in a different class than someone who has the money to invest in a business and employ other people.
Discussions about class in the US arise from the mid-20th century creation of a middle class, a category created by the struggle for stable, unionized jobs with good salaries and benefits. Today, as costs rise and wages remain stagnant, the markers of “middle-classness” that this position once afforded—like buying a home or getting a degree—are increasingly supported by massive debt. And the original “middle class” excluded many workers, such as Black people and women, from economic safety, so income levels and wealth and assets remain lower for these groups today.