What’s a dating scan??

I see people talking about it and I’m curious. I know I’m scheduled for one Thursday I’ll be 36 weeks. But from what my doc said it seem like it’s an appt were they see how Big baby is and after they do a few swabs of my front and back. But on my other appointments they usually measure my belly and baby HR, they say baby is measuring 39 weeks at my last appt. I’m curious do a dating scan determine if they induce you early? or idk.