On top, the URL with the tracking identifier shown inside the box. Underneath, what the URL will look like with the new feature
In Private browsing on Safari, the Link Tracking Protection feature will work when you’re making your way through the internet from website to website. On Mail and Messages, Link Tracking Protection will remove a tracking identifier when you click on a link.
A tracking identifier is made up of a unique series of letters and numbers which means each identifier is connected to one device. With this tracking tag, advertisers can send personalized ads to a particular device which means that when you have the Link Tracking Protection feature enabled, the ads you receive might no longer seem relevant to you.