Sonogram VS Ultrasound??

Elizabeth
I went to a doctor to confirm PCOS and got an ultrasound done. Well, I just got the bill and am paying (out of pocket) $115 for the ultrasound and $30 for a 3D sonogram, as stated on the bill... and I'm wondering what the difference between the two was. I was under the impression I only had an ultrasound. So what distinguishes an ultrasound from a sonogram?