foreskin

esinahka The retractable fold of skin encompassing the most nerve-dense tissue in the human male, which naturally covers and protects the head of the penis.

And the uncircumcised man child whose flesh of his foreskin is not circumcised, that soul shall be cut off from his people; he hath broken my covenant.  — Genesis 17:14, the Christian Bible.

In primates, the foreskin is present in the genitalia of both sexes and likely has been present for millions of years of evolution. (quote-book)

"The foreskin has two main functions. Firstly it exists to protect the glans penis. Secondly the foreskin is a primary sensory part of the penis, containing some of the most sensitive areas of the penis." - The Royal Australasian College of Physicians

The female clitoral hood is homologous with the foreskin.