https://motherboard.vice.com/en_us/article/bjpx3w/what-are-data-brokers-and-how-to-stop-my-private-data-collection

Going about your daily business—shopping online, buying a home, getting married, using a search engine, liking a Facebook page, registering to vote—leaves an enormous paper trail, and data brokers are scooping it up.

Data brokers are entities that collect information about consumers, and then sell that data (or analytic scores, or classifications made based on that data) to other data brokers, companies, and/or individuals. These data brokers do not have a direct relationship with the people they're collecting data on, so most people aren't even aware that the data is even being collected.