No Follow is a term used to instruct a search engine crawler not to follow a link to the destination and subsequently not pass any weight through it.
It is a link relation used to form part of the markup of a link on a web page. For example:-
On it’s own:
<a href="/page.html" rel="nofollow">This is my nofollowed link</a>
How its rendered: This is my nofollowed link