Astroturfing is an artifice that uses either a specific demographic or a diverse group of people to push a political agenda, often without their knowledge. Astroturfers incite others to action by spreading disinformation or talking points aimed at disseminating a specific message either for or against a specific politician, political organization or piece of legislation.
Astroturfers are most often highly paid lobby groups or political operatives, who act at the behest of an organization or individual with a stake in the successful outcome of the astroturf campaign. A successful astroturf campaign can sometimes emerge into a genuine "grassroots" movement and most astroturf campaigns are not discovered and/or discredited until long after the campaign is over.
-- Nancy Pelosi
"Denver photojournalist El Marco was at the event and has an amazing pictorial essay detailing how Pelo[si]’s Astroturf brigade had to be coached by professional organizers — including several day laborers who didn’t speak English and couldn’t tell what the signs they were holding read."
-- Michelle Malkin