Shadow libraries (also pirate libraries or black open access) are online repositories of freely available digital media that are normally paywalled, access-controlled, or otherwise not readily accessible.

Shadow libraries usually contain textual works like academic papers and ebooks, and may include other digital media...software...

Anna's Archive, Library Genesis, Sci-Hub, UbuWeb and Z-Library are some of the most popular shadow libraries for books and academic

https://en.wikipedia.org/wiki/Shadow_library