This 空 character means empty and available in Japanese. This is used in the context of an empty parking space or a vacant hotel room.
CJK Ideographs are characters used in Chinese, Japanese and Korean languages. Their writing systems all completely or partly use Chinese characters.
📅 Japanese “Vacancy” Button was approved as part of Unicode 6.0 in 2010
under the name “Squared CJK Unified Ideograph-7a7a”
and added to Emoji 1.0 in 2015.