open house 
noun
1A place or situation in which all visitors are welcome: our basement is an open house for other kids [mass noun]: they kept open house, entertaining a wide variety of writers...
- He kept open house in his office, a small, single-storey building at the mouth of the Salang Valley.
- Here she kept open house for the traveller the poor and those in need of help.
- The new music organisations kept open house to new developments, enabling New York audiences to hear the latest Stravinsky, Schoenberg or Webern at a time when recordings of this repertoire had barely begun.
1.1North American An open day.FRAG is a main source of public input for us, but we also host annual open houses where the public can come and ask us questions, and we speak to schools and community groups about what we are doing....
- It also has public meetings and open houses set for this month.
- In contrast, few people attend open houses or public meetings, several councillors noted.
1.2North American & Australian /NZ An occasion during which a dwelling that is for sale may be viewed by prospective buyers without an appointment.So I would stomp around these open houses glaring at anyone who looked like an evil investor and we ended up renting for another year and then moving in with mum and dad....
- I've known of a few people who didn't intend to change houses, but just popped into a neighbourhood open house out of curiosity.
- I have now been three years in my humble home and continue to laud the day I decided to come to the open house.