In particular, vacant housing is either for sale, for rent, rented or sold, for occasional use, or held off market.
Categories for held off market include forclosure, personal/family reasons (which includes e.g. units where the owner moved into assisted living or is currently living elsewhere with family), legal reasons (e.g. divorce or code violations), preparing to rent/sell, held for storage of household furniture, needs repair, currently under repair, specific use housing (e.g. dorms), extended absence (e.g. prison), abandoned/possibly condemned, and ‘don’t know’.
Their data tables are broken up kinda weirdly, and each table is its own sheet which is unfortunate to look at on mobile. A ton of things are reported as percents or rates, and I kinda wish they had the detailed raw numbers broken out better.