open house, keep - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Provide hospitality for visitors, as in They loved company and kept open house virtually all summer long. This usage differs from the plain open house, which refers to a particular occasion or period when a home or institution is open to visitors or prospective buyers. [First half of 1500s]