Some starting point for reading about badges and looking for useful definitions:

Antin, Judd, and Elizabeth Churchill. 2011. “Badges in Social Media : A Social Psychological Perspective.” In Proceedings of the 2011 annual conference on Human factors in computing systems CHI 11, Vancouver: ACM, p. 1–4.

EDUCAUSE. 2012. “7 Things You Should Know About Badges.” http://net.educause.edu/ir/library/pdf/ELI7085.pdf (December 20, 2012)

HASTAC Initiative. 2012a. “Badges for Lifelong Learning.” DML Competition. http://dmlcompetition.net/Competition/4/badges-about.php (November 20, 2012).

The Mozilla Foundation, and Peer 2 Peer University. 2012. “Open Badges for Lifelong Learning.” https://wiki.mozilla.org/images/b/b1/OpenBadges-Working-Paper_092011.pdf (November 20, 2012).