A cilice, also known as a sackcloth, was originally a garment or undergarment made of coarse cloth or animal hair (a hairshirt) worn close to the skin. It is used by members of various Christian traditions (including some communicants of the Anglican, Catholic, Lutheran, Methodist, and Scottish Presbyterian Churches) as a self-imposed means of repentance and mortification of the flesh; it is often worn during the Christian penitential season of Lent, especially on Ash Wednesday, Good Friday, and other Fridays of the Lenten season. (source)