What is a dermoid cyst?

A dermoid cyst is a saclike growth that is present at birth. It contains structures such as hair, fluid, teeth, or skin glands that can be found on or in the skin.
Dermoid cysts grow slowly and are not tender unless ruptured. They usually occur on the face, inside the skull, on the lower back, and in the ovaries.  Superficial dermoid cysts on the face usually can be removed without complications. Removal of other, rarer dermoid cysts requires special techniques and training.

http://www.webmd.com/skin-problems-and-treatments/sdermoid-cyst