A Super PAC is a political action committee set up independent of any particular campaign, but able to raise and spend unlimited amounts of money in favor of the election of a candidate, provided the SuperPAC is completely separate from the campaign and the candidate, and not coordinated with them in any way. This is a result of the Citizens United v. FEC decision in January 2010.
Numerous regulations prohibit cooperation between a SuperPAC and a campaign. For example, there is a 120-day moratorium against a Super PAC hiring former employees of a campaign, under a Federal Election Commission regulation.
One effect of Super PACs is to reduce the relative influence of the mainstream media, and enable the public to hear negative information about liberal candidates without liberal censorship.
In the 2016 presidential race, Scott Walker's Super PAC raised $20 million by the end of July 2015, and Jeb Bush's Super PAC raised $103 million. But Scott Walker subsequently pulled out of the race on September 21.
Conservative Solutions PAC supports Marco Rubio, and had raised $16 million by the end of July 2015. A nonprofit organization affiliated with Rubio nonprofit reportedly raised another $16 million.