Which term describes the reflex erection of hairs on the skin?

The term that describes the reflex erection of hairs on the skin is known as the Pilomotor reflex. This reflex is a physiological response triggered by various stimuli, such as cold temperature or emotional arousal, leading to the contraction of the small muscles at the base of hair follicles. As these muscles contract, they cause the hair to stand upright, a phenomenon commonly referred to as "goosebumps."

The Pilomotor reflex is part of the autonomic nervous system, particularly the sympathetic division, which is responsible for involuntary bodily functions. While other types of reflexes exist, such as myotatic reflexes related to muscle length and neurological reflexes concerning the nervous system's overall response patterns, they do not specifically pertain to the reaction of hair follicles. Thus, among the given options, Pilomotor reflex is the most accurate term to describe this specific involuntary reaction.