Impression Share (IS) is the percentage of impressions that your ads receive compared to the total number of impressions that your ads could get.

Impression Share = Impressions / Total Eligible Impressions

Eligible Impressions are estimated using many factors, including price accuracy and itinerary coverage.

Impression Share data is available for campaigns, ad groups and hotel groups. Impression Share is a good way to understand whether your ads might reach more people if you increase your bid or budget.