Oral malodor has many etiologies. The use of accurate descriptor terms to describe this condition facilitates its clinical diagnosis and treatment by health care professionals. Oral malodor, a generic descriptor term for foul smells emanating from the mouth, encompasses ozostomia, stromatodysodia, halitosis (both pathological halitosis and physiological halitosis) and fetor oris or fetor ex ore. These latter terms, in turn, denote different sources of oral malodor. The terms ozaena, fetor narium, dysosmia, hyperosmia, cacogeusia, and dysgeusia are also related to oral malodor, and assist in accurately describing a clinical presentation. Systemic pathological states, such as diabetes mellitus, uremia and hepatic diseases, induce metabolic products that are detectable as oral smells. Local oral conditions produce volatile sulphur compounds and other breakdown products that intensify oral malodors. The clinical labelling and interpretation of different oral malodors both contribute to the diagnosis and treatment of underlying disease. This article stresses the relationship between smell and taste, emphasizes specific meanings for related oral malodor terms, reviews smell comprehension and indicates some of those commonly-encountered associated clinical conditions.