Saint Nicholas Day, also called the Feast of Saint Nicholas, is observed on December 6 (and/or its eve on December 5) in Western Christian countries, and on December 19 in Eastern Christian countries.
It is the feast day of Saint Nicholas of Myra. It falls within the season of Advent. It is celebrated as a Christian festival with particular regard to Saint Nicholas’ reputation as a bringer of gifts, as well as through attendance at church services. (Source)
St. Nicholas Day is not a public holiday. Businesses have normal opening hours.