Areola is the dark region surrounding the nipples. The areola can be small or large, round or oval. It can honestly be of any size. The areola can change in shape, size and color over the life span due to hormonal changes in your body. The areola has mall bumps on them which are either hair follicles or Montgomery glands. Montgomery glands are small oil glands that lie under the skin and provide lubrication during breastfeeding.
Sources:
https://www.verywellhealth.com/parts-of-a-nipple-and-areola-430642
https://www.healthline.com/health/womens-health/large-areola#why-size-fluctuates