Unique scans are one of the real-time scan metrics included with every account. While total scans includes every scan your code has received, unique scans only includes the number of scans from unique users.
For example, if John scans your code 5 times, and Sally scans your code 2 times, you would have 7 total scans, but only two unique scans, because Sally and John are unique users. You can find this metric on the right side of the My Codes dashboard, or by clicking into an individual code.