The frenulum is an elastic piece of skin that connects the foreskin to the glans on the underside of the penis. Its role is to ensure that the foreskin tightens around the glans and stays in place.
The frenulum is also known as the frenulum of prepuce of penis.
More About Frenulum
In certain cases, the frenulum is so tight that it needs to be removed in order to completely free the glans from the foreskin. The frenulum on both circumcised and uncircumcised penises is extremely sensitive. It is thus a popular point for stimulation and pleasure, especially through oral sex. However, its high sensitivity requires that some stimulation happens before touching the frenulum directly, just like women require some foreplay before the clitoris can be stimulated.