A follicle is a small, sac-like structure in the body that plays a crucial role in various biological processes. In the context of hair, a hair follicle is the part of the skin that produces hair and anchors it in place. Each follicle contains a hair bulb, where hair growth begins, and is surrounded by a network of cells and blood vessels that nourish the hair. In the reproductive system, follicles are found in the ovaries, where they contain immature eggs, or oocytes. During the menstrual cycle, certain follicles mature and release an egg during ovulation, a key event in human reproduction. This process is regulated by hormones such as estrogen and luteinizing hormone.