Vacancy rate is the percentage of vacant units in comparison to all the units in the property.
Vacancies
Total Units
An example would be if a hundred unit property had 5 vacancies, the property would have a 5% vacancy rate.
As mentioned in the Vacancy blog, one could purchase a property at a discount, due to a high vacancy rate, solve the reason for the vacancy, fill the vacant units, and then have a more valuable property.
This is a continuation of a serious entitled: The Top 10 Terms of Commercial/Investment Real Estate.