: Puzzles are grouped into 5 main folders (A through E) and subdivided into 495 specific PGN files by ECO code.
The phrase refers to a popular community-curated dataset where millions of Lichess puzzles are organized into zip files based on their Encyclopedia of Chess Openings (ECO) codes . What the Zip Files Contain
: These are designed for offline training or for use in external chess software (like Scid vs. PC) where users want to drill tactics that arise from their own opening repertoire. Where to Find the Data