December 21 isn't just four days before Christmas for many in Australia. It's “Gravy Day,” inspired by one of the most unlikely Christmas songs ever written. Singer Paul Kelly's 1996 composition “How to Make Gravy” is one of that country's most popular holiday songs, even though its setting is a letter written from a prison inmate to his brother, ostensibly to pass along a recipe for the family's Christmas dinner. In the lyrics, the narrator is writing on the 21st of December — now “Gravy Day.” Australian Prime Minister Anthony Albanese mentioned “Gravy Day” this week in his explanation for releasing five drug smugglers who had been in prison for nearly two decades.