The term 'sinus cavity' refers to the hollow cavities in the skull that are filled with air and lined with mucous membranes. The sinuses are connected to the nasal passages and help to humidify and filter the air we breathe. The antrum is a specific type of sinus cavity located in the maxillary bone, which is the largest bone in the face. It is responsible for producing mucus and helping to regulate air pressure in the sinuses.