Öskudagur, also known as Ash Wednesday, is the final day of the Icelandic Shrovetide celebrations. It falls on the day after Sprengidagur (Fat Tuesday) and marks the beginning of Lent. Öskudagur is observed in Iceland and other countries as a day for various customs, including dressing up in costumes and participating in processions.

One prominent tradition on Öskudagur is the custom of children and sometimes adults dressing up in costumes and going from house to house to sing songs or perform small acts in exchange for candy or small treats. This tradition is somewhat similar to Halloween in other cultures. The costumes can range from traditional Icelandic outfits to more contemporary and imaginative choices.

The name "Öskudagur" is derived from the Icelandic word "öskur," which means ashes. In some places, people might also attend church services on Ash Wednesday, where ashes are traditionally used in a symbolic way, marking the sign of the cross on the foreheads of the faithful as a sign of penance and reflection.