According to Wikipedia, Genius is “an online media knowledge base founded on October 2009 by Mahbod Moghadam, Tom Lehman, Ilan Zechory. The site allows users to provide annotations and interpretation of song lyrics, news stories, sources, poetry, and documents.”
From their about page:
What is Genius?
Genius breaks down text with line-by-line annotations, added and edited by anyone in the world. It’s your interactive guide to human culture.