Final answer:
The process of inserting a single needle into a hair follicle for hair removal is known as electrolysis. It is a more permanent method of hair removal compared to depilation, as it destroys the hair root.
Step-by-step explanation:
Inserting a single needle into a hair follicle for hair removal is called short-wave electrolysis, or simply electrolysis. This method of hair removal involves using an electrified needle to destroy the hair root, which prevents the hair from growing back. Unlike depilation, which only removes hair above the skin or temporarily removes part of the hair, electrolysis offers a more permanent solution by targeting the hair follicle itself.