What is a lingual frenum?
The lingual frenum refers to the fold of soft tissue located under the tongue, joining it to the base of the mouth. Everybody has a lingual frenum and they will all appear different to one another.
An example of a lingual frenum in a baby's mouth, highlighted by the yellow circle. Shutterstock Images.

An example of a lingual frenum in a child's mouth, highlighted by the yellow circle. Shutterstock Images.
There are a number of frenum's present in the mouth. For example, the labial frenum that can be seen when lifting the upper and lower lips. Frenums are present from birth.