Ad position is the order in which an ad is displayed on a search engine results page (SERP). For example, ad position "1" means the ad is displayed first on the webpage.
Google no longer provides this info in the AdWords platform. However, the ad position is actually a formula based on several factors.
Your CPC bid, ad quality including landing page, how competitor the Google auction is at that time, the context of the search query, and the ad extensions (sitelinks, tel#, etc.)