A benign or low malignant potential cystic epithelial neoplasm composed of cells which contain intracytoplasmic mucin. It may arise from the ovary, pancreas, appendix, and lung. The disease is mucinous cystadenoma (MONDO_0006859). Also known as: adenoma, mucinous, benign, mucinous adenoma, mucinous cystoma, pseudomucinous cystadenoma.