Facebook collects a lot of data about each of its users e.g. through their Facebook profiles. Many of the users have provided more data in their profiles than they realize. Users can already be profiled based on basic data such as age, gender, and location. Most people also like content that they find interesting and browse the Facebook pages of companies, artists or even dog breeds. These make it easy to determine what the user likes. When data about your locations, shopping and friends and their browsing is added to this data, Facebook knows you better than you do.
In addition, Facebook may collect limited data through your browsing history when cookies are allowed. Almost all companies have a Facebook tracking code installed on their websites, which sends data about page views to the advertiser’s Facebook account. It’s no coincidence that when you browse travel companies’ websites you will be targeted with travel-related advertising on Facebook.