The term 'Christmas in Calais' refers to a famous World War I Christmas truce that occurred on December 25, 1914. During this truce, British and German soldiers laid down their arms and celebrated Christmas together in the French city of Calais. The crossword solutions for this term are 'NOEL, ' which is the French word for Christmas. This term is often used in carols and other holiday songs to refer to the birth of Jesus Christ.