Estimation of the maximum traffic that a site can generate on a keyword / group of keywords. This indicator is internal to the tool and based on a multiplication of the search volume and click rate from the 1st position of a result.
Calculation: Click rate of position 1 * Search volume
My site is 3rd on the "assurance" keyword which has a search volume of 10000 (10000 users type this keyword each month).
The click rate of the 1st position is 15%.
So, the maximum traffic estimate is 10,000 * 15 / 100 = 1,500 visits per month while the traffic estimate would be 10,000 * 11 / 100 = 1,100 visits