to become less crowded; to thin out; to get empty
to be hungry
「空く」 has another reading with different meanings.
to open (e.g. doors)
to get hungry; to become hungry
席が空いたので座りました。
A seat became vacant so I sat down.
お腹が空いて困っています。
I'm in trouble because I'm hungry.
部屋が空くまで待ちます。
I will wait until the room becomes vacant.