What is this called? Is it normal?

I'm 36 weeks pregnant, and I know that swelling in the calves, ankles, and feet is normal, but I poked my leg (for some odd reason), and I noticed that the dent in my calf never went away. It's been 30 minutes and it's smaller but still there... It's kind of freaking me out because it's never happened before. Can anyone give me any information on this?