Not to be confused with aureola.
The word areola is used to describe a small circular area. While it is most commonly used by far to describe the coloured area surrounding the nipple, it can be used to describe other areas such as the area of redness surrounding a pimple.
This contrasts with a nipple which is the thing that points up from the breast that does not include the areola around it even though both are the same colour.
There is a reason for the areola being a different colour to the rest of the breast. The areola is roughly where the ducts of the milk secreting glands are. If you look carefully around a nipple, you might see 15-20 small openings arranged radially around the tip of nipple (lactiferous ducts) where milk is released from during lactation. Other small openings in the areola are sebaceous glands which may provide a little oily lubrication during lactation, otherwise known as Montgomery's glands (or glands of Montgomery).
The other reason areolas exist, of course, is because they make the female breasts more sexually appealing.
Normal areolar colour ranges from light pink to dark brown with races with lighter skin tones tending to have paler areolas and races with darker skin tones to have darker areolas. Areolar colour changes to a darker shade during pregnancy. Some regression to the original colour may occur thereafter but part of the change is permanent. Normal areolar size ranges from pretty small to holy cow.
I wonder if anyone's ever named their daughter "Areola" ... perhaps someone from a non-English speaking background ... does it mean anything in some other language?