The times gone past; the good old days.
[Scots : auld, old + lang, long + syne, since.]
"Auld Lang Syne" (Scots pronunciation: [ˈɔːld lɑŋˈsəin]: note "s" rather than "z") 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 (and other) countries and is often sung to celebrate the start of the New Year at the stroke of midnight. By extension, its use has also become common at funerals, graduations, and as a farewell or ending to other occasions.
The song's Scots title may be translated into English literally as "old long since", or more idiomatically, "long long ago", "days gone by" or "old times". The phrase "Auld Lang Syne" is also used in similar poems by Robert Ayton (1570–1638), Allan Ramsay (1686–1757), and James Watson (1711) as well as older folk songs predating Burns. Matthew Fitt uses the phrase "In the days of auld lang syne" as the equivalent of "Once upon a time..." in his retelling of fairy tales in the Scots language.