In internet marketing, Ad Rank refers to the position of a PPC ad (pay-per-click) on the SERP (search engine results page).

The ranking, or position, of your ad depends on the position of each keyword in the ad.  

So how is the position of each keyword determined? 

The rank of each keyword is determined by your bid for that keyword or ad group multiplied by the matched keyword’s Quality Score.

Keyword Rank = Your keyword bid x the matched keyword’s Quality Score

In a nutshell, the more relevant your keywords, ad text (ad copy), and landing pages are, the higher your Quality Score and Ad Rank.  

Higher Ad rank typically yields a better position on the SERP and a lower CPC (cost-per-click) and is the result of higher CTR (click-through-rate).