It's a narrowing of the lower esophagus that can cause difficulty swallowing (dysphagia). The narrowing is caused by a ring of mucosaltissue or muscular tissue Patients with this rings can develop intermittent difficulty swallowing or, more seriously, a completely blocked esophagus.
Schatzki ring or Schatzki–Gary ring is a narrowing of the lower esophagus that can cause difficulty swallowing (dysphagia).