rel="nofollow" this is the code of nofollow u will find it in source page, this means telling search engine robots do not follow this links.
"Nofollow" provides a way for webmasters to tell search engines "Don't follow links on this page" or "Don't follow this specific link." Originally, the nofollow attribute appeared in the page-level meta tag, and instructed search engines not to follow (i.e., crawl) any outgoing links on the page. For example: <meta name="robots" content="nofollow" />
Actually, search engines do "follow" nofollow links...they just don't count them towards the target url's link popularity.
If you know what PageRank is or Link Juice, if you put a link with nofollow it doesn`t transfer any of PR or Linkk juice