Tongue Tie

"Some babies are born with a condition known as ankyloglossia or "tongue-tie", which is a structural abnormality of the lingual frenulum (a connective tissue underneath the tongue). A baby with tongue-tie actually has a frenulum that is too short and hinders tongue movements upward, outward, and/or to either side of the mouth. A person who is born with tongue-tie faces a wide variety of problems with eating, speech and language, drooling, and dental problems. Tongue-tie often looks very different from one case to another, so it's possible that a doctor may not notice it during a neonatal physical exam. Some babies are born with a tongue-tie that is fairly easy for doctors to recognize, but many cases go undiagnosed to cause future developmental problems. "

- From "Special breastfeeding situations: is my baby tongue-tied?"

Other Sources:

"Tongue Tie: from confusion to clarity" - TongueTie.Net

"Fact Sheet: Tongue-Tie (Ankyloglossia)" - EntNet.Org