I think the term "for rent" might mean different things to different people. I read that as "apartments listed as being available to rent to the public (e.g. on

I think the term "for rent" might mean different things to different people. I read that as "apartments listed as being available to rent to the public (e.g. on apartments.com) with no signed contract for anyone to move in". Which I would think would be one of the primary reasons for vacancy. Meanwhile, your source seems to say some houses shouldn't be counted vacant because they are 2nd, 3rd or 4th houses, or are listed on AirBnB as short term rentals, all of which I would classify as vacant. I know 1/6 vacant homes are a second home in SF (according to the YouTube video). But I would agree with you that apartments that will be empty for < 1 month as turnover happen makes no sense to classify as vacant, assuming that the new renter is identified.