It's explained just down there I think vv

A penis whose stretched flaccid length is more than approximately 2.5 standard deviations below average size for the age group but otherwise formed normally is referred to in a medical context as a micropenis.

The smallest penis on record was reported in a medical journal by researchers from Oxford University's Department of Physiology, Anatomy and Genetics. The researchers noted that patient "Alfred," a male musician, in his early 30s, from Oxfordshire, UK., "possessed a penis almost indistinguishable from a clitoris." Currently there is much debate in the medical community as to whether patient "Alfred" is actually male or intersexed.