These are servers that help peers (users) find each other to share pieces of a file.
While the original site is gone, the "Torrentz spirit" lives on through various clones and newer meta-search alternatives. Understanding the Meta-Search Concept
Downloading from public indexers carries risks like malware or legal notices from your ISP.
Unlike standard torrent sites, a meta-search engine like Torrentz searches across multiple "trackers" simultaneously.
Most modern sites use these instead of actual .torrent files. They are essentially a "digital fingerprint" that tells your torrent client what to find without needing to download a separate small file first. Essential Safety Checklist
How to Download Torrents Safely: The Best Torrent Client & Settings