The feast of St. Nicholas is held on December 6 each year and is more popular and acknowledged in Europe. A German tradition calls for children to put a boot outside the front door on the night of December 5 to December 6. In theory St. Nicholas fills the boot with small gifts and also checks up on the children to see if they were good. If not they will have a tree branch in their boots instead.
This is a quaint and very cute tradition that is observed in many parts of the world and is a lead up to the bigger celebration of Christmas.
In our family, we have been observing this tradition since our children were quite small and we often refer to it as "Santa's dry run", sort of a tune up for the reindeer.
Find out more about St Nicholas at wikipedia.