clocking in SEO:

A website that returns altered webpages (different contents) to search engines crawling the site is known as cloaking. In other words, a human reading the site would see different contents or information than a search engine robot/crawler reading the site.

Most of the time, cloaking is implemented in order to improve search engine ranking by misleading the search engine robot into thinking the content on the page is different than it really is.

Cloaking can be a dangerous method of getting listed in the search engines and may not be recommended

REF:

http://www.webtoolhub.com/tn561346-cloaking-checker.aspx