A frenum is a naturally occurring muscle attachment, normally seen between the front teeth (either upper or lower). It connects the inner aspect of the lip with the gum.
A lack of attached gingiva, in conjunction with a high (closer to the biting surface) frenum attachment, which exaggerates the pull on the gum margin, can result in recession. Additionally, an excessively large frenum can prevent the teeth from coming together resulting in a gap between the front teeth. If pulling is seen or the frenum is too large to allow the teeth to come together, the frenum is surgically released from the gum with a frenectomy. A frenectomy is simply the surgical removal of a frenum.