From a YouTube post:
"Auld Lang Syne" is a Scottish poem written by Robert Burns in 1788 and set to the tune of a traditional folk song (Roud # 6294). It is well known in many English-speaking countries and is often sung to celebrate the start of the new year at the stroke of midnight on New Year's Day.
The song's (Scots) title may be translated into English literally as "old long since", or more idiomatically, "long long ago" or "days gone by". The phrase "Auld Lang Syne" is also used in similar poems by Robert Ayton (15701638), Allan Ramsay (1686-1757), and James Watson (1711) as well as older folk songs predating Burns. In his retelling of fairy tales in the Scots language, Matthew Fitt uses the phrase "In the days of auld lang syne" as the equivalent of "Once upon a time." In Scots syne is pronounced like the English word sign.