Final answer:
The flagellum is the hair-like tail region of the sperm, which aids in its mobility to reach the egg for fertilization.
Step-by-step explanation:
The hair-like tail region of the sperm is called the flagellum.
This tail-like structure enables the sperm to swim through the female reproductive tract in order to reach and potentially fertilize the egg. The head of the sperm contains the nucleus with the male's genetic material, while the midpiece is packed with mitochondria to provide the energy needed for the movement of the flagellum.