What is online tracking?
Read the page on online tracking written by the Federal Trade Commission (FTC) of the US: Online Tracking | Consumer Information – consumer.ftc.gov
Also worth checking: Understanding browser tracking written by the Goodwill Community Foundation (GCF) – edu.gfcglobal.org
– Cookies (in particular third-party cookies) – link
– Flash cookies (becoming obsolete as of 2018, since Flash Player is widely abandoned) – link
– Web beacons (or tracking pixels) – link
Links worth checking out
My personal recommendations to defend against online tracking
Here are some infographics. While they contain some useful information, don’t do everything they say (such as installing Adblock Plus, instead opt for uBlock Origin).
Click on the image for full-size.