Flatfoot (pes planus) is a condition in which the longitudinal arch in the foot, which runs lengthwise along the sole of the foot, has not developed normally and is lowered or flattened out. One foot or both feet may be affected.
Children as well as adults may be flat-footed. Most children are flat-footed until they are between the ages of 3 and 5 when their longitudinal arch develops normally.