In short, a follicle is an organ that produces hair across the body. While similar in composition, the shape of hair follicle will differ in different parts of the body and will dictate the texture of the hair that grows from it – e.g. the difference between the hair on your head and the hair in your pubic area.
While hair follicles go through phases of growth and rest (which is perfectly normal); inactive hair follicles come about when the follicle in question ceases to enter the growth phase and the hair is no longer growing from the pore.
So if you’re looking to grow your hair you need to stimulate the follicle to give it the best chance of growth.