Unique Clicks = the unique users who click any link
Link Clicks = how many times each one of those uniques users clicked.
Outbound Clicks = how many times a user clicks a link and leaves Facebook (i.e. visits your website)
Ferris Bueller clicks five links across all of your ads in the given reporting period.
Day 1: Ad1 - clicks Learn More and goes to your website
Day 7: Ad2 - clicks Shop Now and goes to your website
Day 15: Ad3 - clicks Like on your ad
Day 17: Ad4 - clicks Learn More and goes to your website
Day 28: Ad5 - clicks Sign Up and fills out a Lead Form on Facebook
Unique Clicks = 1
Link Clicks = 5 (Ad1, Ad2, Ad3, Ad4 and Ad5)
Outbound Link Clicks = 3 (Ad1, Ad2, and Ad4)