What does impression share indicate about a product group?
- It provides an average benchmark of all similar products from other retailers
- It shows your product group impressions relative to other product groups in the same campaign
- It shows how many impressions your product group has received divided by the estimated number it was eligible to receive
- It predicts your product group’s future impressions
Impression share (IS) is the number of impressions you’ve received divided by the estimated number of impressions you were eligible to receive. Eligibility is based on your current ads’ targeting settings, approval statuses, bids, and quality. Data is available at the campaign, ad group, product group (for Shopping campaigns), and keyword levels.
Read more here: https://support.google.com/adwords/answer/2497703?hl=en