Noun: Scout, a member of the Scouts movement (i.e. Boy Scouts, Cub Scouts or Girl Scouts).
Partiolainen comes from partio (”patrol,” ”scouting”) + -lainen (a suffix which can be combined with a name to form an adjective for a member of an organization or other defined group, a follower of philosophy etc.).
For more than 60 years, the Guides and Scouts of Finland have been selling advent calendars around the Christmas season. You may see Scouts selling them on the street or in shopping malls or door to door for about 7 € to support their organization.
Scout Advent Calendar (Partiolaisten adventtikalenterikampanja).