Frenulum

A frenulum (or frenum, plural: frenula or frena, from the Latin frēnulum, "little bridle", the diminutive of frēnum) is a small fold of tissue that secures or restricts the motion of a mobile organ in the body.

Frenula on the human body include several in the mouth, some in the digestive tract, and some connected to the external genitalia.

An overly short oral or genital frenulum may require a frenulectomy or frenuloplasty to achieve normal mobility.

The word frenulum also refers to a bristle present at the root of the hindwing of most moths which engages with a small hook on the forewing (the retinaculum) to join the wings together.

...
Wikipedia