Wikipedia
Julebukking (Gå julebukk) is a Christmas tradition of Scandinavian origin.
Between Christmas and New Year's Day, people wearing masks and costumes (Julebukkers) would go door to door, where neighbors receiving them attempt to identify who is under the disguise. In one version of Julebukking, people go from door to door singing Christmas songs. After they have sung, they are usually awarded with candy. Another tradition requires that at least one person from the visited household join the band of Julebukkers and continue to the next household.
In certain aspects, the custom resembled the modern-day tradition of Halloween trick-or-treating. Julebukkers will often disguise their voices and body language to further the masquerade. Offering people holiday treats and something to drink is customary. Once identities are known and the food is eaten, the Julebukkers continue to the next home.