The sinus cavity refers to a group of air-filled spaces located within the bones of the face and skull. These cavities are connected to the nasal passages and help to lighten the weight of the skull, improve voice resonance, and produce mucus that keeps the nasal passages moist. There are four main pairs of sinus cavities: the frontal sinuses, maxillary sinuses, ethmoid sinuses, and sphenoid sinuses. Each of these sinuses has a specific location and function, contributing to overall respiratory health and comfort by filtering and humidifying the air we breathe.