Final answer:
Microcephaly is when the head circumference is smaller than average, based on specific measurements. It can be characterized by various physical features.
Step-by-step explanation:
The condition described refers to microcephaly, which is a medical term used to describe a head circumference that is smaller than average. In this case, the criteria used to diagnose microcephaly is when the shortest anterior-posterior diameter is less than 10 cm, or if the greatest diameter is less than 12 cm.
Microcephaly can be identified through various physical characteristics, such as a smaller-than-average eye opening, skin folds at the corners of the eyes, a low nasal bridge, a short nose, and a smaller-than-average midface size. Additionally, individuals with microcephaly may have a thin upper lip and an indistinct philtrum.