Sinusitis, also known as a sinus infection or rhinosinusitis, is inflammation of the sinuses resulting in symptoms.Common signs and symptoms include thick nasal mucous, a plugged nose, and pain in the face.Other signs and symptoms may include fever, headaches, poor sense of smell, sore throat, and cough. The cough is often worse at night. Serious complications are rare.inusitis (or rhinosinusitis) is defined as an inflammation of the mucous membrane that lines the paranasal sinuses and is classified chronologically into several categories: 1  Acute rhinosinusitis – A new infection that may last up to four weeks and can be subdivided symptomatically into severe and non-severe.