On the Internet a digital footprint is the word used to describe the trail, traces or "footprints" that people leave online. This is information transmitted online, such as forum registration, e-mails and attachments, uploading videos or digital images and any other form of transmission of information — all of which leaves traces of personal information about yourself available to others online.
(Webopedia definition)
Digital Citizenship Adventures - Managing your Digital Footprint This classroom activity could help students understand how they are projected on the Internet and the possible consequences of their digital footprint.
Internet Society - Your Digital Footprint Matters There are 9 online tutorials available for students to help them make the right choices about their digital footprint.