If you hear the term "black company", what kind of company do you imagine? As we all know, black is the darkest color, so if you pictured an evil company with a dark side then you would be on the right track. A black company (aka "black corporation" or "black business") is buraku kigyō ブラック() 企業(きぎょう) in Japanese. In general, it is a term used to refer to an unacceptably exploitative employment system.
Now, maybe you're thinking this is a word to describe a factory somewhere in China, but you'd be wrong. The term is actually usually associated with white-collar industries rather than blue-collar ones. It was coined by young IT workers in the early 2000's and, being the IT workers that they were, spread this nickname around the internet as an internet meme. Now, thanks to its fame, it is a term that can be used for other industries that are not IT.
As the popularity of the term grew, the black company problem received more and more attention in Japan. In 2009, a drama film called "A man on the verge at a BLACK company" was released. It was based on an office worker who started a 2ch thread about the black company he worked at. This company's ruthless and unethical work environment was duplicated in the film.