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1.
A #hashtag used on Twitter, Facebook at other social media that is conceived by a business or organization to promote a product, issue, event position, or goal in a way that seems to have been spawned by a "grass roots" movement.

Sometimes called "astroturf tags," these symbolic tokens are often created by professional public relations firms or their media consultants as part of a broader public awareness (or propaganda) campaign. Many social media users, generally interested in the topics that the tags seem to represent, will often start using the tags in their own messages, unaware of the corporate, private, or other agendas that may lie behind them.
The Grass Tag #energyTomorrow was created by the American Petroleum Institute to spam twitter with pro-energy industry propaganda.
by shoqvalue October 16, 2010