1. A condition, situation, or event in which a home is open and welcome to visitors at any time. We like to have an open house, so please just drop by whenever you like. It really threw the neighborhood off-kilter the way the Jeffersons kept open house, with people arriving and departing at all hours.

2. A time or state in which a house, apartment, or other residential building that is up for sale may be viewed by prospective buyers. We've been looking for weeks for the right house to buy, but there's an open house this Saturday for one that looks really promising.

3. A specified day in which an organization, especially a school, university, or business, is open for visitation, inspection, or evaluation by members of the public. Primarily heard in US. I wouldn't mind the open house at school so much if we didn't have to act like trained seals for the prospective parents.