The tongue web is the frenulum under the tongue. The extent of its development varies greatly from person to person. Some people may have webbing that extends nearly to the tip (making them "tongue tied"), and others may have no visible web at all.
The tongue webbing can be cut for tongue lengthening (see tongue frenectomy for more on that) or to make room for tongue splitting or a tongue piercing, and it can be pierced as well (see tongue web piercing).
This webbing can complicate some procedures such as tongue piercing if it is especially pronounced.