The kind of activism undertaken when you "do something" about a problem by tweeting or posting links to Facebook, without any intent of ever actually doing something. Nothing more than a nonsense feelgood gesture so that one can say they "did something about" whatever trendy cause they're pretending to care about. Usually only lasts a week or two before the cause is completely forgotten (i.e. it stops being cool to forward/retweet on the subject).
I forwarded a video about some unspeakable atrocities in a country I didn't know existed until I watched the video. My hashtag activism is going to accomplish something!