So, pretty much, Teratoma(germ-cell type tumor) translated to greek mean "Monstrous Tumor". This is because the teratoma class of tumor tends to have tissue structure, like the picture would suggest (hair, teeth, nails and sometimes more complex things like eyes, brain or other organs), thusly making it look "monstrous". It is thought that these tumors are present at birth, though generally not diagnosed until later in life.
If you want to know more, I suggest:
Teratoma - Wiki
eMedicine - Teratoma article by Chad A. Hamliton