Think (for example) "spontaneous" protests by groups of people all waving the same signs and wearing SEIU shirts.
Cheers!
Instead of the Tea Party being a real "grass roots" movement the Dems declared it "astro-turfed" as in fake grass.
The Dems themselves do this quite a bit. They use the term among themselves, for example, to describe when they bus in hundreds of union workers ordered to go to give a political show for a liberal cause, a fake grass roots gathering.