open house

Short definition from Wiktionary

Noun

1. 1
   A house habitually kept open to callers.
2. 2
   An event, often in one's home, at which there are few restrictions regarding who and how many may attend.
3. 3
   An event during which a facility or institution is open to the public for inspection or tour.
4. 4
   A period of time, usually several hours in a day, during which a house which is for sale is open for inspection or tour by interested parties.
5. 5
   A casual school event where the school invites parents or guardians to tour their child's school and meet the teachers.