Definitions for "Unique Click"
AKA "unique visitor" - each visitor to a website in a 24 hour period is considered to be a unique click. If the same person visits a website twice in 24 hours they still only count as one unique click, no matter how many pages they view. For example, Joe Surfer clicks one of your sponsor links and goes to the tour you've decided to send him to. He looks at 3 pages on the tour, then comes back 6 hours later and looks at three more pages. In total, Joe's visits would show up in your stats as 6 raw clicks and one unique click.
a click generated by a different computer
a single click by a single user