A condition with damage to the lining of the lower esophagus resulting from chronic acid reflux (esophagitis, reflux). Through the process of metaplasia, the squamous cells are replaced by a columnar epithelium with cells resembling those of the intestine or the salmon-pink mucosa of the stomach. Barrett's columnar epithelium is a marker for severe reflux and precursor to adenocarcinoma of the esophagus. [MeSH]