The phrase "real nipple" is typically used to refer to an actual, natural nipple of a human or animal. It distinguishes from artificial or fake nipples, which may be used for various purposes like bottles or toys. Full definition
The nipples are designed with great care, using feedback from mothers and experts, to feel just like real nipples so as to make the transitioning from breastfeeding to bottled milk easier for the baby. (tinyfry.com)
Some babies have a difficult time going back and forth from artificial nipple to real nipple and this can affect how they are latching on and removing the milk. (themilkmeg.com)
(It can be a real nipple, bottle nipple or pacifier). (easybabylife.com)