From Garrison Keillor:
It was on this day 98 years ago that the word "grassroots" made its debut as a political term. On this day in 1912, Senator Albert Jeremiah Beveridge of Indiana was on stage at the Progressive Party Convention when he proclaimed: "This party has come from the grass roots. It has grown from the soil of people's hard necessities."
In the almost hundred years since, "grassroots" has become a popular buzzword and an influential campaign strategy. The word refers specifically, according to the OED, to the "rank and file of the electorate or of a political party." With grassroots campaigns, you often see people standing on street corners holding clipboards, collecting signatures for petitions, or setting up information tables on college campuses and neighborhood farmers' markets, or posting fliers around town, or holding political meetings at people's houses, sometimes potluck-style.
There's now even a term for faking a grassroots movement: It's called "astroturfing," after that artificial grass found at sports stadiums. It's when powerful lobbyists masquerade as individual citizens, using the tactics of grassroots campaigns, but hiding their affiliation or real agenda. The term was coined by U.S. Senator Lloyd Bentsen, after he got a bunch of letters in the mail from concerned citizens urging him to promote the interests of the insurance industry.