Almost every website uses website visitor tracking for advertising, analytics or other purposes. Usually, websites track users by putting a cookie banner in place that pops out for the first time a user visits the website. It asks for user consent to collect data in order to personalize his browsing experience for the next visit to the same website.
Cookie Banner from CookieScript example
Before letting cookies track visitors, websites must inform the visitors about the tracking, if they want to stay compliant with different privacy laws worldwide. Users also should be given an option to opt out of tracking if they do not wish to share personal data. Tracking how visitors act on a website can be really helpful for your website to grow. You can track what pages of your website have the most clicks, track how many users are willing to share their personal information, such as IP address, and modify your Cookie Banner based on that.
Tracking also happens from website to website - that is called cross website tracking. It is a process when the user’s actions on the internet are tracked from website to website and social media platforms usually are involved in it. For example, if a website puts a Facebook widget onto one of its pages, it allows the company to track user actions on that particular website.
Cross website tracking wouldn't be possible without third-party cookies that come together with external parties which place their adverts or other widgets on the website you’re visiting.