“Dark money” consists of political contributions from sources that aren’t revealed before voters go to the polls. The “money” is"dark” because the public doesn’t know where it’s coming from. The term “dark money” appears to have been coined by the Sunlight Foundation in October 2010. The magazine Mother Jones has a regular column on Dark Money, but it appears that the Sunlight Foundation used the term before Mother Jones.
 
“Dark money” meaning “secretive money” has also been used before 2010, but usually as a banking term and not as a specific political term.
 
   
Wikipedia: Dark money
Dark money is a term for funds used to pay for an election campaign without proper disclosure before voters go to the polls. If an election is held and “dark funds” helped sway the voters, it is termed a dark election. Funds can be spent on the behalf of a candidate running in an election, or to influence voting on a ballot question.
 
Etymology
The term “dark money” appears to have been coined by editors at Mother Jones Magazine to describe undisclosed funds that were used during the United States 2010 mid-term election. When paired, the two words “dark” and “money” accounted for the fact that voters were denied the knowledge of large campaign contributions and in kept in the dark. When used in common speech, the term is generally intended to imply that money can have a sinister side similar to the “Force of the dark side” from Star Wars.
 
During the 2012 US Presidential election at least one major news paper, The Boston Globe, also began to use the term. The originators of the term, Mother Jones magazine, described the “dark money” of that election as originating from a “secretive coterie” of donors that powers a “Lovecraftian monster that moves from State to State, dissolving the foundations of the Republic that originates.”
   
Sunlight Foundation
OUR MISSION
The Sunlight Foundation is a nonprofit, nonpartisan organization that uses the power of the Internet to catalyze greater government openness and transparency, and provides new tools and resources for media and citizens, alike. We are committed to improving access to government information by making it available online, indeed redefining “public” information as meaning “online,” and by creating new tools and websites to enable individuals and communities to better access that information and put it to use.
 
We want to catalyze greater government transparency by engaging individual citizens and communities—technologists, policy wonks, open government advocates and ordinary citizens –- demanding policies that will enable all of us to hold government accountable. Sunlight develops and encourages new government policies to make it more open and transparent, facilitates searchable, sortable and machine readable databases, builds tools and websites to enable easy access to information, fosters distributed research projects as a community building tool, engages in advocacy for 21st century laws to require that government make data available in real time and trains thousands of journalists and citizens in using data and the web to watchdog Washington.
   
OCLC WorldCat record
Reckless! : how debt, deregulation, and dark money nearly bankrupted America (and how we can fix it!)
Author: Byron L Dorgan
Publisher: New York : St. Martin’s Press, 2009.
Edition/Format:   Book : English : 1st ed
(This is a different concept of “dark money.” Pg. 5: “It was a period of what I call dark money filled every crevice of the financial world. Outside of public view, the financial engineering of bizarre new risky, complex products grew and grew.”—ed.)
 
OCLC WorldCat record
Top producer : a novel of dark money, greed, and friendship
Author: Norb Vonnegut; Mel Foster
Publisher: [Old Saybrook, Conn.] : Tantor Media, 2009.
Edition/Format:   eAudiobook : Fiction : EnglishView all editions and formats
Summary:
In the wake of a man’s graphic murder in front of hundreds of party-goers, the victim’s best friend, investment expert Grove O’Rourke, is entreated by the man’s widow for help, a situation that is further complicated by a dark secret and an expensive cover-up.
 
Sunlight Foundation—Blog
Daily Disclosures
by Bill Allison Oct. 18, 2010, 12:43 p.m.
A roundup of what we’re noticing in the Reporting Group as we dig into government data and disclosures:

Dark money: Of the 202 outside organizations spending money to influence the 2010 mid-term elections, just 93 of them have disclosed donors to Federal Election Commission. Some of the organizations may be disclosing donor information to the Internal Revenue Service. Keep checking the Reporting Group website for further details.
 
Sunlight Foundation Reporting Group
Dark money: Super PACs fueled by $97.5 million that can’t be traced to donors
By Ryan Sibley Oct 20 2010 11:31 a.m.
Of the $189 million spent so far by Super PACs, non-profits and labor unions to influence the 2010 mid-term elections, $97.5 million has come from groups that do not disclose any donors, an analysis of Federal Election Commission contribution records shows. That is, about 52 percent of the money spent so far on everything from political ads to phone banks to fliers promoting or opposing federal candidates has come from groups that don’t disclose the sources of their funds.
 
Sunlight Foundation—Blog
Follow the dark money: Secret donors target Obama’s old seat
by Bill Allison Oct. 28, 2010, 3:54 p.m.
Illinois Senate Democratic candidate Alexander Giannoulias, hoping to hold the seat that was once occupied by President Barack Obama for his party, has been the target of more attacks funded by undisclosed donors than any other candidate—more than $4.4 million, according to a preliminary review of disclosures that explicitly state whether a candidate is supported or opposed by an outside group.
 
USA Today
Election reflections
Updated 11/3/2010 1:53 PM
(...)
By far the most pernicious element in this is the rising pool of dark money — the untraceable contributions of unlimited size that pour into attack ads. It often comes through non-profit groups incorporated like those that shelter the homeless or promote cancer awareness. And it provides a vehicle for wealthy individuals, companies or lobbying groups to fund anonymous attacks on a candidate who does not vote to their pleasure.
   
UPI.com
Published: Nov. 14, 2010 at 3:30 AM
‘Dark’ money clouds the political waters
After a U.S. Supreme Court ruling back in January opened the floodgates for unrestricted corporate and union spending in political campaigns, what started out as a mere trickle grew into a deluge of outside money by the time midterm elections arrived with a crash Nov. 2.
By MICHAEL KIRKLAND
WASHINGTON, Nov. 9 (UPI)—After a U.S. Supreme Court ruling in January opened the floodgates for unrestricted corporate and union spending on political campaigns, what started out as a mere trickle grew into a deluge of outside money by the time midterm elections arrived with a crash Nov. 2.
 
Much of the tens of millions of dollars raised as a result of the ruling has been “dark”—donors not identified.
 
Mother Jones
Dems Eye Legal Attack on Shadow Spending Groups
Lawmakers and interest groups are crafting a strategy to challenge the tax status of dark money outfits like Karl Rove’s Crossroads GPS.
By Andy Kroll | Fri Jan. 28, 2011 4:00 AM PST
Democrats in Congress fighting to blunt the effects of the Supreme Court’s Citizens United decision face an uphill battle in the 112th Congress.
   
TPM
Super-PACs and Dark Money: ProPublica’s Guide to the New World of Campaign Finance
July 11, 2011, 2:52PM
by Kim Barker and Marian Wang, ProPublica
The nation is gearing up for yet another “most expensive election in history,” the quadrennial exercise in which mind-numbing amounts of money pour into the political system. But this year promises more than just record spending—more money will be flowing from more players with more opportunities to hide the source.
 
OCLC WorldCat record
Dark money in politics
Author: Bill D Moyers; Clara Jeffery; Monika Bauerlein; Thomas Frank; Public Affairs Television (Firm); All authors
Publisher: [United States] : Public Affairs Television, Inc. ; 2012.
Edition/Format:   DVD video : English
Summary:
Episode guests: Mother Jones editors Clara Jeffery and Monika Bauerlein, historian Thomas Frank.
       
Boston (MA) Globe
Ruling allows major political donors to hide identities
February 15, 2012|By Brian C. Mooney
When the Supreme Court ruled two years ago that corporations could make unlimited political donations, the justices probably did not have in mind big checks from paper corporations operating from an address at a postal box or an accounting firm.
 
It’s one aspect of a phenomenon known as “dark money’’ to super PACs that help specific candidates even though they technically operate independently. The other shade of dark money involves funds flowing to super PACs from several tax-exempt “social welfare’’ advocacy groups, which do not disclose any information about donors. 
   
Salon
THURSDAY, MAR 8, 2012 03:28 PM CST
The GOP’s new love of “dark money”
In 2000, it was Republicans like McCain and Castle—not Democrats—who were pushing for donor disclosures
BY JUSTIN ELLIOTT, PROPUBLICA
Last month, when House Democrats introduced the DISCLOSE 2012 Act to try to stop the flow of secret “dark money” into the electoral process, it marked an ironic twist.
 
Mother Jones
It Takes Dark Money to Make Dark Money
Karl Rove’s dark-money group doles out $2.75 million to an outfit fighting to keep dark money in the dark.
—By Andy Kroll | Fri Apr. 20, 2012 3:00 AM PDT
When Crossroads GPS, the conservative nonprofit started by GOP political gurus Karl Rove and Ed Gillespie, isn’t dropping millions of dollars on anti-Obama ads, it’s doling out tens of millions more to like-minded groups. “The ATM of the Right,” Politico recently called Crossroads. Between May 2010 and December 2011, new tax records show, Crossroads gave $4 million to Grover Norquist’s Americans for Tax Reform and $500,000 to former Sen. Norm Coleman’s American Action Network, among others.