Ultrasound vs. Sonogram

I may be the only person who did not know this, but I was wondering why some people call it an "ultrasound" and others call it a "sonogram." I thought they were interchangeable terms, but now I see they arent! So I'm having an ultrasound, but the actual picture is a sonogram. I think.....

What is the difference between an ultrasound and a sonogram?

"An ultrasound is the machine that allows you to see your baby during your pregnancy. A sonogram is the picture taken of your baby during the ultrasound. A sonogram is a "still-shot" of your baby. 4D Ultrasounds take 3D ultrasound images, or 3D sonograms, and adds the element of time to the process. The result: Live Action ultrasound images of your baby. Some people refer to the procedure as prenatal imaging, 3D imaging, a 3D scan, or 4D scan."
- www.4d-ultrasounds.com