Opening book
An opening book is a database of opening moves and positions that an engine or program consults to play known theory quickly, instead of calculating each early move from scratch.
Also called: book
An opening book stores the moves that strong players have chosen in the early stages of the game. A program that has a book can answer a known position immediately, saving time and avoiding weak early choices. Books are also used by human players in the sense of repertoire files, which hold the lines they plan to play.
The usefulness of a book is that it reflects accumulated experience. Moves in the book have usually been tested in many games, so they are rarely poor. Some books include statistics on how often each move was played and how it scored, which helps you see what is popular and what is rare.
For your own study, a book is a starting point, not a substitute for understanding. Memorizing long lines without knowing the plans behind them leaves you stranded as soon as the opponent leaves theory. Learn the main ideas, the typical pawn structures and the usual middlegame plans of your openings, and use a book or database to check the details. Deviations from the book in your games are valuable moments to study afterwards.
Also worth reading is Opening explorer. An opening explorer is a tool that shows, for any position reached from the start, which moves players have chosen in past games and how often each move led to a win, draw or loss.
Compare it with Endgame tablebase. An endgame tablebase is a precomputed database that gives the exact result and best moves for every position with a small number of pieces, so engines can play those endgames perfectly.
Computer terms such as "Opening book" are most useful next to a coach who reads your games with you, which is how a first lesson with George Li works.
Related terms
The opening is the first stage of a chess game, running from the starting position until most pieces have left their home squares and the kings are safe, and it shapes what kind of middlegame both players will face.
Opening theory is the body of knowledge about the opening, made up of the known moves, plans and evaluations of the main lines that players have tested over many games.
An opening repertoire is the personal menu of opening lines a player has decided to rely on, so that with either color they know where they are heading and have answers ready for the opponent's most likely choices.
Opening preparation is the work done before a game to know your chosen lines well, including studying your own repertoire and checking the likely choices of a specific opponent.
An opening explorer is a tool that shows, for any position reached from the start, which moves players have chosen in past games and how often each move led to a win, draw or loss.
A chess engine is a computer program that searches positions and evaluates moves, usually playing and analyzing far stronger than any human, and it is used for analysis, preparation and play against a machine.
Guides that go further
What to decide first, the questions to ask, what a first lesson should show and the red flags to avoid.
How much does chess coaching cost?
Published rates for private, group and subscription chess coaching, with the source and the date of each.
A game review, a read on your level and a written study plan from George Li.
Want to spot this in your own games?
A first lesson starts with your games: George reviews them and builds a study plan around what he finds.