An abscess (i.e., a circumscribed area of pus or necrotic debris) localized in the area surrounded by the deep fascia of the neck including the pharynx, larynx, trachea, upper esophagus, thyroid, and parathyroid glands. Infections of pharyngeal, tonsillar, and laryngeal origin affect this space, which includes the parapharyngeal and retropharyngeal spaces. [from
HPO]