The definition of an open house is an opportunity where a home, school or other normally restricted area opens its doors and allows people to visit for a period of time.(noun)
When you are trying to sell your home and you schedule a time between 1 and 4 PM on a Sunday for people to come and walk through the house, this is an example of an open house.
See open house in Webster's New World College Dictionary
See open house in American Heritage Dictionary 4
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