Traditional Scottish Air from the early 1700s (or earlier??) used to bid farewell to the old year at the stroke of midnight. The song's Scots title can be translated into standard English as "old long since" (or “long, long ago”). Singing the song on Hogmanay or New Year's Eve very quickly became a Scots custom that soon spread to other parts of the British Isles. As Scots (not to mention English, Welsh and Irish people) emigrated around the world, they took the song with them.

Should old acquaintance be forgot,
and never brought to mind?
Should old acquaintance be forgot,
and old lang syne?

CHORUS:For auld lang syne, my dear,
for auld lang syne,
we'll take a cup of kindness yet,
for auld lang syne.

And surely you’ll buy your pint cup!
and surely I’ll buy mine!
And we'll take a cup o’ kindness yet,
for auld lang syne.

CHORUS

We two have run about the slopes,
and picked the daisies fine;
But we’ve wandered many a weary foot,
since auld lang syne.

CHORUS

We two have paddled in the stream,
from morning sun till dine†;
But seas between us broad have roared
since auld lang syne.

CHORUS

And there’s a hand my trusty friend!
And give me a hand o’ thine!
And we’ll take a right good-will draught,
for auld lang syne.

CHORUS

Source: https://en.wikipedia.org/wiki/Auld_Lang_Syne