…a form of advocacy in support of a political, organizational, or corporate agenda, designed to give the appearance of a “grassroots” movement. The goal of such campaigns is to disguise the efforts of a political or commercial entity as an independent public reaction to another political entity—a politician, political group, product, service or event. The term is a derivation of AstroTurf, a brand of synthetic carpeting designed to look like natural grass.
from Wikipedia.com