The Urban Dictionary defines Slactivism (they spell it with a "k," but that seems like a lot of extra work) as "The act of participating in obviously pointless activities as an expedient alternative to actually expending effort to fix a problem." Wikipedia cites awareness bracelets, internet petitions, and magnetic car ribbons as a few examples. I first read the term at Snopes.com several years ago, but I'm too lazy to dig through the site (and it's annoying pop-ups) to find the article. Basically, it's doing something that takes very little effort and is ultimately useless, but makes us feel like we're doing a good thing.
Perhaps my favorite example of Slactivism is the "repost this" meme. You know, the messages that say something like "I think it's wrong to use midgets to club baby seals. If you agree, please repost this message." The best thing about these memes, in my opinion, is their paradoxical nature. On the surface, they make it seem like we're taking a moment out of our obsessive narcissism in order to make the world a better place. At the same time, the idea that the world is going to change because you posted something to Facebook is hubris at its most absurd.
When a particular "repost this" message show up enough to annoy me, I'll change the wording a bit to make it stupid before reposting, mainly just to see if anyone notices. Because the internet makes it incredibly easy to do really retarded things (and because I often get bored at work), I've decided to start posting a new (and dumb) "repost this" meme to Twitter, theoretically on a daily basis. Check them out at https://twitter.comSlactivismDaily. And if you agree with me, please repost.