Torrentz (originally Torrentz.eu) was a legendary meta-search engine for BitTorrent that famously shut down in 2016. It didn't host files itself but instead indexed millions of torrents from other popular sites, acting as a massive, fast, and simple directory for the community.
While the original site is gone, the "Torrentz spirit" lives on through various clones and newer meta-search alternatives. Understanding the Meta-Search Concept
How to Download Torrents Safely: The Best Torrent Client & Settings
These are servers that help peers (users) find each other to share pieces of a file.