What does a lump behind the left ear mean?

My mom showed me tonight a large lump under her left ear and it was red and kinda swollen. She has been sick lately and very congested. She thinks its nothing but im worried about her!! She just noticed it and said it hurt when she moved her jaw and her ear just aches! I'm really scared. She said if it doesn't go away in a couple days then she will go to the doctor. Anyone have an idea of what it might be? If u think its cancer then what kind?