Click-throughs represent a) campaign instances, and b) marketing channel instances.
a) Campaign instances reflect the number of times that a tracking code for a given campaign was passed into reporting. When a visitor clicks on an affiliate link that has been tagged with one of these tracking codes, the visitor is taken to your landing page and the tracking code is captured in s.campaign. That data is sent into reporting and a click-through is recorded.
b) In the context of marketing channels, click-throughs are the number of times a hit was bucketed into a marketing channel.
Click-through rate is the way to measure a web advertisement's effectiveness. The click-through rate occurs when a user follows a hyperlink (usually a web advertisement).
Click-throughs in data warehouse are called "campaign views."