Plato's belief on Soul. Is it eternal or immortal?

My professor said that Plato's belief on the soul is: "It is eternal". I have been researching wheather it's true or not. The belief originated from the Egyptians. Socrates, his teacher believed that the soul is IMMORTAL. Why do some people say that in Plato's perspective that the soul is ETERNAL? What is the correct and philosophically valid information on this?