Natural Search Results
Search engine results which are not sponsored, or paid for. Also called Organic search results.

Navigation
The links within a website to help user's interaction as simple and efficient as possible. A site’s navigation links all the pages together.

Navigation bar (nav bar) 
A web site's navigation icons, usually arranged in a row down the left hand side or along the top that play a crucial role in directing spiders to the site's most important content and in getting site visitors to go deeper in the site.

Negative Keyword (AdWords term)
Negative Keyword is a form of keyword matching. The advertiser can specify search terms they do not want their ad to be associated with.

Nofollow
A command found the HTML code of a web page which instructs robots not to follow either any links on the page or a specific link. Often used to prevent a link from passing link authority and commonly used on sites with user generated content like in blog comments.

Noframes Tag 
Alternative non-framed HTML on a frameset page for very old, non-frames capable web browsers and search engine spiders. Placing good keyword rich text in noframes tags is a good idea if your site is framed.

Noindex
A command found in the HTML code of a web page which instructs robots to not index the page or a specific link.

Non Reciprocal Link
If site “A” links to site “B”, but site “B” does not link back, this link is considered non reciprocal. Search engines tend to give more value to non-reciprocal links than to reciprocal ones.