Friction ridges are
|“||[t]he ridges present on the skin of the fingers and toes, and on the palms and soles of the feet, which make contact with an incident surface under normal touch. On the fingers, the distinctive patterns formed by the friction ridges that make up the fingerprints.||”|
These ridges are sometimes known as "dermal ridges" or "dermal papilla." Friction ridges are formed in utero during fetal development, and even identical twins do not have the same fingerprints.