Target impression share is an automated bidding strategy that sets bids with the goal of showing your ad on the absolute top of the page, on the top of the page, or anywhere on the page of Google search results. This strategy can be used to raise awareness of your brand and build campaigns that are focused on branded terms. If you’re unable to devote a lot of time to daily bid management, you can use this automated bidding.

Read More here: https://support.google.com/google-ads/answer/9121108