A millionaire is a person who resides in a household whose net worth or wealth exceeds that of "one" million United States dollars, Euros, British pounds or units of a comparably valued currency. A centimillionaire has a net worth of more than 100 million units of currency (even though the SI prefix "centi" mean one-hundredth, not one hundred).

In many countries or cultures, a certain level of prestige is associated with being a millionaire, which makes that amount of wealth a goal for many. However, due to inflation, the status of millionaire is no longer as exclusive as it once was, and so other descriptions, like multi-millionaire or billionaire have come into use to describe the highest levels of individual wealth. The increasing number of millionaires is partially due to inflation: a million dollars, for example, provides far less purchasing power today than it did in the 19th century. However it still ensures a comfortable lifestyle for those becoming millionaires.