Ad Clicks: The number of times monitored ads have been clicked on during the chosen time period.
Unique Visitors: The number of different visitors that the arrived to your landing pages after clicking a paid ad.
Remember that one unique visitor may click on an ad multiple times, accounting for the difference between these two parameters. So if a single visitor clicks an ad 6 times you will see 1 unique visitor and 6 ad clicks.
If you have any questions about this process, feel free to reach out to our 24/7 chat support.