Glossary
Net worth
Everything you own minus everything you owe.
Assets - cash, investments, property, business equity - minus liabilities - mortgages, loans, credit card balances. It is the number that "millionaire" actually refers to, and it is not the same as income.
Two people earning $300,000 can have net worths of $2m and negative $80,000. Income is the input; net worth is the score. Tracking it quarterly is the single most useful habit in personal finance.