Rank is a comprehensive measure of website popularity and profitability. It can be estimated the following way:
First, you got to know positions of the site for different search queries in Google organic search results.
Second important notion is traffic – estimated number of visitors coming to the page from Google organic search results.
Third, you should know traffic cost – estimated cost of purchasing visitors.
Combining these three values, position, traffic and traffic cost for each query, you get website rank value!
The higher the rank is, the more popular and profitable the website is.