The page a Google ad's click lands on, after any tracking. Its domain is the one the ad shows as its display URL.
Every Google Ads ad has a final URL: the address of the page people reach after clicking it. It's separate from the tracking an advertiser adds. Tracking goes in the tracking template and the final URL suffix, and with parallel tracking the browser goes to the final URL while the tracking runs in the background.
Google's Destination requirements tie the rest of the ad to it. The display URL takes its domain from the final URL, the final URL shouldn't send people on to another domain, and the tracking template has to lead to the same content.
- Your own ads' final URLs are your pages. So are those of anyone allowed to link straight to you.
- Google's trade mark restrictions follow the second-level domain of the final URL, not the account.
- The Ads Transparency Center doesn't show final URLs, but searching it for your web address finds the advertisers whose ads point there.
When an ad you don't recognise shows your address, its final URL is very likely your site, and the question is whose tracking sits in front of it. The explainer on ads that show your address goes through the fields.
Google's own help and policy pages first.