Original: The word frenulum on its own is often used for the frenulum of prepuce of penis, which is an elastic band of tissue under the glans penis that connects to the prepuce, or foreskin to the vernal mucosa, and helps contract the prepuce over the glans.
Simplified: This is an elastic band of tissue under the glans penis that connects to the prepuce, or foreskin to the vernal mucosa.