is one of the most recognized web addresses for Library Genesis (LibGen) , a massive "shadow library" that provides free access to millions of academic papers, textbooks, and general-interest books.

LibGen stores the that Sci-Hub (the pirate academic paper site) delivers. When a user requests a paper via Sci-Hub:

: It acts as a secondary backing store for sites like Sci-Hub, allowing researchers to bypass expensive journal subscriptions.