Citizens United v. Federal Election Commission (FEC) is a 2010 Supreme Court case that struck down federal limits on independent expenditures by corporations and labor unions. An independent expenditure is money spent on ads or other messages that support or oppose a candidate, without coordination with that candidate's campaign.
A nonprofit, Citizens United, made a film about Hillary Clinton in 2008 while she was running for president. It wanted to put the film on cable on-demand right before the primaries.