Lobbying: The act of attempting to influence decisions made by officials in government, most often legislators or members of regulatory agencies.
Political Action Committees (PACs): These are organizations that pool campaign contributions from members and donate those funds to campaigns for or against candidates, ballot initiatives, or legislation.
Grassroots Movements: These are movements driven by the constituents of a community. It's based on people "on the ground" using collective action from the local level upward.