The song beginning “Should auld acquaintance be forgot” is “Auld Lang Syne.”
The Scottish poet Robert Burns wrote down a version of the song in 1788, drawing on older Scots verses and a traditional melody. The title means roughly “old long since,” or more naturally, “for old times’ sake.”
The song became strongly associated with New Year's Eve, especially through performances and broadcasts in the English-speaking world. Its lyrics are often sung imperfectly because the Scots vocabulary is unfamiliar, and many people know only the opening verse and chorus. The melody is used for farewells and commemorations as well as New Year's celebrations.