A digital footprint refers to the trail of data a person leaves online through their internet activity, including websites visited and information submitted. There are two types of digital footprints - active, which is deliberately shared through actions like social media posting, and passive, which is collected without awareness through things like IP addresses and browsing data. Digital footprints matter because the information can be permanent, taken out of context, or exploited by cybercriminals. Some ways to protect a digital footprint include limiting shared data, checking privacy settings, and using search engines to audit online information sources that mention you.