Under the Ads tab there is a column that says: % served. Then for each add it shows a percentage, what does this information mean? Thanks!
It stands for the percentage of impressions served by the ad, relatively to the total amount of impressions for the same ad group. (For a given date range)
% served is the amount of times that particular ad was shown for keywords impressions in the adgroup that ad has been. Example: Say you have 20 impressions for the Ad Group and Ad1 served is 50%, which means the ad1 was shown 10 times out of the 20 impressions.