"Billionaire" is the debut single by American recording artist Travie McCoy, featuring guest vocals from Bruno Mars. It is the lead single from McCoy's debut studio album Lazarus. The song was produced by The Smeezingtons, which consists of Mars, Philip Lawrence and Ari Levine. Lyrically, McCoy imagines what would happen if he became a billionaire, referencing all the good he would do to others with the money along with his desire to be on the cover of Forbes magazine, "smiling next to Oprah and The Queen". As of July 2011, the song has sold 3,000,000 digital downloads, making it Mars' third 3-million-seller.

Bruno Mars came up with the lyrical concept for "Billionaire" during a trip to London in which he was given $350 by his record label to spend for 11 days. He found the amount of money to be insufficient, and explained "We were like, 'Is this the biggest mistake we've ever made? We thought we were broke in California; what are we going to do here?' So we've got no money, and I'm walking the streets and came up with, 'I wanna be a billionaire, so freakin' bad.'" With the song, McCoy intended to avoid "superficial" lyrics in the wake of an economic recession, and added "There’s something to sing about here; if I was in the position to have a ridiculous amount of money, would I be selfish or selfless?’ I just took that concept and ran with it."

A billionaire, in countries that use the short scale number naming system, is a person who has a net worth of at least one billion (1,000,000,000) units of a given currency, usually the United States dollar, the euro, or the pound sterling. Forbes magazine updates a complete global list of known U.S. dollar billionaires every year.

According to the Forbes report released in March 2012, there are currently 1,226 U.S. dollar billionaires worldwide, boasting a combined total net worth of $4.6 trillion. The United States is home to 425 billionaires, while Russia and China have 96 and 95 billionaires respectively. Among U.S. billionaires, the average age is 66 years.

In countries that use the long scale number naming system, a billionaire would have one million million (1,000,000,000,000) units of currency. Under the short scale number naming system, an individual with such a fortune would be a trillionaire. There are no known euro or U.S. dollar trillionaires – in U.S. dollars, such a fortune would be roughly equivalent to the entire 2010 gross domestic product of Mexico. However, some individuals have attained fortunes of over one trillion units in other currencies. According to VnExpress, 9 Vietnamese had stock market assets valued at over one trillion đồng (US$47.5 million) by the end of 2011. According to The Korea Herald, there were 16 Koreans with stock market assets valued at over one trillion won (US$895 million) on March 9, 2012. According to the Jakarta Globe, 116 Indonesians had assets worth over one trillion rupiah (US$117 million) in 2011.

In music, a song is a composition for voice or voices, performed by singing. A song may be accompanied by musical instruments, or it may be unaccompanied, as in the case of a cappella songs. The lyrics (words) of songs are typically of a poetic, rhyming nature, though they may be religious verses or free prose.

A song may be for a solo singer, a duet, trio, or larger ensemble involving more voices. Songs with more than one voice to a part are considered choral works. Songs can be broadly divided into many different forms, depending on the criteria used. One division is between "art songs", "pop songs", and "folk songs". Other common methods of classification are by purpose (sacred vs secular), by style (dance, ballad, Lied, etc.), or by time of origin (Renaissance, Contemporary, etc.).

A song is a piece of music for accompanied or unaccompanied voice or voices or, "the act or art of singing," but the term is generally not used for large vocal forms including opera and oratorio. However, the term is, "often found in various figurative and transferred sense (e.g. for the lyrical second subject of a sonata...)." The noun "song" has the same etymological root as the verb "to sing" and the Oxford English Dictionary (OED) defines the word to mean "that which is sung" or "a musical composition suggestive of song." The OED also defines the word to mean "a poem" or "the musical phrases uttered by some birds, whales, and insects, typically forming a recognizable and repeated sequence and used chiefly for territorial defence or for attracting mates."