A millionaire is an individual whose net worth or wealth is equal to or exceeds one million units of currency. 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.
Many national currencies have, or have had at various times, a low unit value, in many cases due to past inflation. It is obviously much easier and less significant to be a millionaire in those currencies, thus a millionaire (in the local currency) in Hong Kong or Taiwan, for example, may be merely averagely wealthy, or perhaps less wealthy than average. A millionaire in Zimbabwe in 2007 could have been extremely poor. Because of this, the United States Dollar (USD) is the most widely used currency standard to compare the wealth of people all over the world. Hence a person must have a net worth of at least one million USD to be recognised as a millionaire anywhere in the world.
As of June 2020, there were estimated to be just over 13 million millionaires or high-net-worth individual (HNWIs) in the world. The United States had the highest number of HNWIs (4,700,000) of any country, while New York City had the most HNWIs (348,000) among cities..
The word was apparently coined in French in 1719 to describe speculators in the Mississippi Bubble who earned millions of livres in weeks before the bubble burst. (The standard French spelling is now millionnaire, though the earliest reference uses a single n.) The earliest attestation in the Oxford English Dictionary (OED) is a letter of Lord Byron of 1816, which mentions it as a French term needed because of the "Lilliputian" value of francs. Earlier English writers also mention the French word, including Sir William Mildmay in 1764. The OED's first print citation is Benjamin Disraeli's 1826 novel Vivian Grey, The anglicisation millionary was used in 1786 by Thomas Jefferson while serving as Minister to France; he wrote: "The poorest labourer stood on equal ground with the wealthiest Millionary".
While statistics regarding financial assets and net worth are presented by household, the term is also often used to describe only the individual who has amassed the assets as millionaire. That is, even though the term statistically refers only to households, common usage is often in reference only to an individual.