Click Tracking - Counting the number of clicks that a link achieves through a counter program..

Cloaking - A spam trick generally used to get search engine positions. Different pages are displayed depending on the circumstances.

CPA (Cost Per Action) - Payment by the advertiser websites for advertising only if the visitor buys something.

CPC (Cost Per Click) - Amount paid by the websites to search engines for the number of visitors send to them by the search engines on the basis of per click.

Crawler - A Spider that downloads multiple pages from the same domain.

Crawling - The spider that look for links in the pages (urls) it downloads and then crawl down through the domain.

Cross Linking - The inner linking among a group of domains those are owned by a single individual. This is often done for increasing link popularity.

CSS (Cascading Style Sheets) - Simple and common display styles usually added to webpages.