What is a sinus? Author: admin A sinus is a hollow space in a bone, organ or tissue. The para nasal sinuses are air pockets within the bones of your face. You have four pairs that are located above, below and to the outside of your eyes and to the side of your nose. These air file Last modified:11-12-2009, 6:56 pm Number of views:598 Ketan C. Mehta, MD Diplomate, certified by American Boards of Internal Medicine, Pulmonary Medicine and Critical Care Medicine. Disclaimer