• Anomaly in which one or more of the arches of the feet are flat.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2025
• (flat foot) An anatomic deformity in which the arch of the foot collapses, resulting in the entire sole of the foot coming into complete or near-complete contact with the ground.
  NCI
  U.S. National Cancer Institute, 2021
• (pes planus) A foot where the longitudinal arch of the foot is in contact with the ground or floor when the individual is standing; or, in a patient lying supine, a foot where the arch is in contact with the surface of a flat board pressed against the sole of the foot by the examiner with a pressure similar to that expected from weight bearing; or, the height of the arch is reduced.
  Human Phenotype Ontology (HPO)
  The Human Phenotype Ontology Project, 2025
• Flatfoot, congenital or acquired flatness of the longitudinal arch of the foot. Usually associated with loss of the arch is a rolling outward of the foot and heel, resulting in a splayfoot position. Normally the arch is maintained by the shape of the bones and by the ligaments and muscles of the...
  Encyclopedia Britannica
  Encyclopedia Britannica, Inc., 2025