Is a ratio of number of users who click on a specific link to the number of users that view a page, email or advertisement. Higher ranked webpages generally have a higher click-through rate, with ads correlating well with the content of the page. The general purpose of a click-through rate is to gauge how well your ads and keywords are performing.
Cloaking is a black hat strategy that displays two different types of webpages to humans and bots. They are separated and identified via IP addresses. The Bots are served with fake or artificial content packed with keywords and false information that will boost the website's rankings. The humans are given real information, but are generally unsatisfied since the content is not what they originaly expected as the website had been artificially boosted. Furthermore there are different levels of cloaking ranging from white hat tactics which are looked upon favorably to black hat tactics which are generally frowned upon.