Everyone has one. A birthday, that is.
And we all know how that traditional song goes... Happy Birthday To You, etc.
But now there's an argument in the US over whether it's owned by a company and people should pay to play it on TV, radio and film or whether it is free because it belongs to the public.
Two years ago, film maker Jennifer Nelson, who was making a film about the Happy Birthday song, was charged $1,500 (£962) to use the track by publisher Warner Chappell.
They claim they own the song's copyright, which gives the owner the right by law to control how a piece of work is used, produce copies of it and charge others to use it for a set number of years.
Now Jennifer wants her money back because she says there's lots of paperwork from the 1920s that suggest no one actually owns the rights to the song.
Warner Chappell disagree and say they spent millions of pounds buying the company that previously owned the song in 1988.
On Wednesday, a US judge will decide whether the song is owned by Warner Chappell or that the Happy Birthday song belongs to the public and should be free to use.
Often called the world's most popular song, it's thought it was written by sisters Patty Smith Hill and Mildred Hill in 1893.
Their song was called Good Morning To All, and over time, the lyrics changed to the "Happy Birthday To You" song we all know today.
In the US, it can now cost anywhere between $500 (£320) and $3,000 (£1900) to play or sing the track on TV, radio or in films.
Sometimes, it can be even higher. Warner Chappell earns an around $2 million (£1.3 million) a year from the money it collects from people using the track.
In the European Union, a club of countries who work together in Europe, it will be free for people to use from 2016.