According to Wikipedia, Earned Media is defined as:

...media "publicity gained through promotional efforts other than paid media advertising...." Additionally, "earned media cannot be bought or owned; it can only be gained organically when content receives recognition and a following through communication channels such as social media and word of mouth.

Within Please Share, earned media is the value that a company associates with clicks generated when their employees share content on Twitter, Facebook, or LinkedIn. 

Within Please Share, companies can define a value for traffic derived from their employee advocacy initiatives. For example, if a company sets a value of $1.73 per click and 10 clicks are generated, the earned media value of that traffic would be $17.30.