What is the definition or description of: sneeze?

Convulsive expulsion: A semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucosa. A sneeze expels air forcibly from the mouth and nose in an explosive, spasmodic involuntary action resulting chiefly from irritation of the nasal mucous membrane. See: http://en.Wikipedia.Org/wiki/sneeze.