Your digital footprint means whereby you have accounts on various websites and upload information about yourself and then maybe as time goes by forget about those sites but the information is still there.
An example is that many people started a Bebo webpage and uploaded images and video of their lives and left it there, months and years later it can still be displayed and also found on search engines.
Employers Google a name before a candidate comes in for an interview, if they see “Johnny in a mess at a party” picture they may not look upon this well as they will be thinking …. will he turn up on Mondays as he has a very busy social life at the weekends etc and might always be hung over……. You have been warned.