Many people are aware that when they go online or visit a website there is a certain amount of tracking going on. This has become even more apparent since the GDPR update which now requires you to get permission off a visitor to track the as the progress through your site.
Apple states that on average there are 6 different trackers on one site all sending data off to third party companies. This date may include information about what browser you are using, where you are on a phone, tablet or computer and where in the world you are located. The locations may be accurate to within the same town or village to where you live. They can also see what interactions you have made with the site, so what pages you have clicked on, what forms you have completed and what products you have bought. All of this data is then feed back to the company to allow them to use it to improve their website and sales experience. Often this data is quite generic, but if allowed, some websites where you have to log in a create an account can get a lot more personal details from you.