Definition:

(noun) : activism (such as signing an online petition) that requires very little commitment or action

Example:

"I had eventually come to the realization that wearing purple, or changing your avatar in support of spirit day, is an act of slacktivism.... Social Media like Facebook and Twitter have provided a space for slacktivism to exist." – blog post by Dan on OutSpokenNYC.com, October 20, 2011