A millionaire is an individual whose net worth or wealth is equal to or exceeds one million units of currency. It can also be a person who owns one million units of currency in a bank account or savings account. Depending on the currency, a certain level of prestige is associated with being a millionaire, which makes that amount of wealth a goal for some, and almost unattainable for others.

In countries that use the short scale number naming system, a billionaire is someone who has at least a thousand times a million dollars, euros, or the currency of the given country (e.g. $1,000,000,000). In contrast, a trillionaire in countries that use the long scale number naming system would be someone who has at least a million times a million units of currency (e.g. $1,000,000,000,000). There is no evidence that anyone on the planet has achieved the latter in either US dollars or euros. The increasing number of millionaires is partially due to prevailing economics, especially inflation; as the individual value of each unit of currency decreases, achieving a million of these becomes easier.