Can someone explain missed miscarriage to me please

I started seeing this term being used recently. I just thought everything was called a miscarriage. From what I'm understanding it's someone who has had an ultrasound or something and find out there's no heartbeat but they haven't miscarried yet? I went to the hospital at 11 1/2 weeks because of some bleeding, I had never had an ultrasound before but when they did one at the hospital they said it showed only around 7 weeks so I was miscarrying. So if my baby had stopped growing for 4 weeks but I didn't find that out until I was miscarrying would it be called a missed miscarriage or just a miscarriage?