A digital footprint, sometimes called a digital dossier refers to the data traces we knowingly or unknowingly leave behind each time we access the internet or other electronic devices. In short, the information about a person that exists on the internet as a result of his online activities.
A common comparison is the footprints you leave behind you when walking along a beach – every step you take leaves an impression on the sandy surface that allows another person to see the marks that your activity has made and offers the possibility for them to follow your trail.
Unlike a beach footprint, a digital footprint trace is often permanent because the companies who own the website in which you input your data also store the information. For example, Google tracks every search made by users, that's over 3.5 billion per day and over 10 exabytes of data, says Cloudtweaks.
This footprint is of two types:
Active footprints are those you leave when you make deliberate choices on the Internet. Facebook, Twitter, blog posts, social network connections, image and video uploads all are among the ways individual's create active digital footprints for themselves.
Passive footprints are those you leave behind without intending to do so. For instance, websites that collect information about how many times you have visited in the recent past are adding to your digital footprint in a "passive" fashion. You don't choose to hand them this data; they collect it when a device at your IP address connects with their websites. Because this is a hidden process, you may not realize it is happening at all.