A teratoma is a rare type of tumor that contains a mixture of tissues, such as hair, teeth, bone, and muscle. These tumors can be benign (non-cancerous) or malignant (cancerous) and can occur anywhere in the body, but are most commonly found in the ovaries, testicles, and near the tailbone. Teratomas are typically formed from germ cells, which are cells that give rise to eggs and sperm.