By Sarah McBride

SAN FRANCISCO (Reuters) - Venture capitalist Ben Horowitz is famous for starting his blog posts with rap lyrics. Now, he will be putting his money into the mix.

His firm, Andreessen Horowitz, announced Wednesday a $15 million investment in Rap Genius, a website using crowdsourcing to dig into and explain arcane details of rap lyrics.

Think of Rap Genius as the Talmud, Horowitz said in a phone interview on Wednesday, referring to the Jewish text that interprets the Old Testament.

As an example, Horowitz cited a Lil Wayne lyric, "real G's move in silence like lasagna." Click on it, and Rap Genius explains the singer is referring to gangsters and the silent g in lasagna.

"If you don't get it, don't be ashamed," reads the Rap Genius note accompanying the line. "?uestlove from The Roots didn't either." Embedded in the note is a Tweet from the musician known as Questlove citing the lyric with the question #AmIGettinold?

The company is slowly spreading to other categories such as literature, political speeches, and science papers.

"We think the community will continue to expand beyond rap into all culture," wrote Horowitz's colleague, Marc Andreessen, in a blog post announcing the investment.

Horowitz first met Rap Genius's co-founders Mahbod Moghadam, Ilan Zechory, and Tom Lehman last year when he visited business mentoring program Y Combinator, which they were attending. The three met as undergraduates at Yale University.

It is not immediately clear how Rap Genius will make money; Horowitz called the company's business model "TBD" (or To Be Determined).

"If they succeed in the mission, and they end up annotating the Internet, there's a huge audience for that," Horowitz said. At that point, a path to revenue would emerge, he added.

Andreessen Horowitz, founded three years ago, announced in January it had raised a $1.5 billion fund, its third. It has invested in some of the country's hottest start-ups, including online bulletin board Pinterest and social-networking site Facebook.

(Reporting By Sarah McBride; Editing by Bernard Orr)

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