Political action group
| How the sausage is made|
A political action group (also, political action committee, or PAC) is an organization formed for the explicit purpose of lobbying the government about a particular issue. Some focus on a very specific issue (like the NRA with gun control), while others are simply broadly left-leaning (such as MoveOn.org) or broadly right-leaning (such as the Club for Growth). The Citizens United ruling has led to the advent of so called Super PACs, which deal with millions of dollars.
Their methods for lobbying politicians include harassing Congressmembers by mass-mailing protest letters to them by the truckload, donating money to politicians and political parties, organizing protests, and producing ad campaigns about an issue.
Super PACs are the mothers of all other PACs, in the sense that they can spend an unlimited amount on their lobbying, with no restrictions on whom they can raise funds from - with the caveat being that they can't directly contribute to the campaign account. That doesn't matter, since they get around this by unloading sprees of negative ads ("attack ads", colloquially) onto a rival candidate to spread their message.