What is "membranous croup"

Croup \Croup\ (kr[=oo]p), n. [Scot. croup, cf. croup, crowp, to croak, to cry or speak with a hoarse voice; cf. also LG. kropp, G. kropf, the crop or craw of a bird, and tumor on the anterior part of the neck, a wen, etc. Cf. Crop.] (Med.) An inflammatory affection of the larynx or trachea, accompanied by a hoarse, ringing cough and stridulous, difficult breathing; esp., such an affection when associated with the development of a false membrane in the air passages (also called membranous croup). See False croup, under False, and Diphtheria.