Nofollow link is exactly vice-versa of dofollow link. These are noncrawling link which are not passed by search engines bot and hence can't be cached or indexed. It is obvious when we wish to prevent a link from crawlingand indexing.

Dofollow link is a kind of hyperlink which says all search engines crawlers to pass through which also put an impact over page rank. When we opt to employ or attempt to achieve a dofollow link then it is counted by search engines and sits in the eye of Google, Bing, MSN, Yahoo etc. as a backlink for your website and

enhances your site ranking