"Nipple size" refers to the physical measurement or dimensions of the nipples, which are the small, usually protruding parts on the breast that allow for breastfeeding in females. Full definition
With the different nipple flow rates to choose from, parents can find what works best for their baby — and change nipple sizes as the baby grows as well. (rookiemoms.com)
I was told it was best to buy this set and then buy a few different nipple sizes because those change as the baby gets older. (goldcoastgirlblog.com)
All of these variations in nipple size and shape are normal, and breastfeeding can be successful with each of these types of nipples. (verywellfamily.com)