Undefined in Chess – definition and usage
Undefined
Definition
In everyday English undefined simply means “not clearly or precisely determined.” In the chess world the word is not a standard technical term like “fork,” “zugzwang,” or “interference.” Nevertheless, the concept of something being undefined does appear in several specialized contexts:
- Computer-chess engine evaluations and tablebases
- Arbiter rulings when a position or situation is not covered by the Laws of Chess
- Compositional stipulations in chess problems where a goal or piece behavior is deliberately left open
- Historical discussions of openings before a generally accepted name or theory has crystallized
Usage in Chess
Although you will not hear a club player say “I played the Undefined Attack,” you can encounter the word in the following practical situations:
-
Engine display:
Some graphical user interfaces (GUIs) show “
--” or the label undefined when the engine has not yet generated a numeric evaluation. For instance, immediately after loading a position with an illegal castling right, Stockfish may first return “undefined” until the internal legality check finishes. - Arbiter decisions: In FIDE competitions, if an irregularity occurs that is not explicitly described in the current Laws of Chess, the arbiter’s task is to determine a remedy. During that deliberation the status of the game could be informally referred to as “undefined.”
- Problem composition: A stipulation such as “Find any undefined piece that mates in two” challenges the solver to decide the identity of a fairy piece consistent with the diagram. The term therefore functions as a creative tool rather than a rule.
Strategic or Historical Significance
Because it is not a mainstream term, undefined carries no direct strategic significance—there is no hidden opening trap. Historically, however, the notion of an “undefined position” emerged in endgame theory long before the digital era. Before databases like Nalimov or Syzygy, analysts sometimes wrote that a study’s outcome was “undefined” when they suspected a draw but lacked a rigorous proof. Modern tablebases have since settled many of those once-uncertain verdicts.
Examples
Below are two concrete illustrations of the word in action.
1. Engine Output Example
Load the following FEN into a GUI with Stockfish but do not let the engine move yet:
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
For a second or two you may see “undefined” or “– –” in the evaluation window,
indicating that the engine has not delivered a centipawn score or mate line.
After a brief calculation the display switches to something like 0.00.
2. Arbiter Scenario
Imagine a rapid-play event in which a digital board freezes and neither player notices that a pawn promotion to a knight has been recorded as a bishop. The resulting material imbalance is discovered ten moves later. Because the Laws of Chess do not spell out this exact equipment malfunction, the arbiter’s first comment in the incident sheet may read “Result undefined pending investigation.”
Interesting Facts & Anecdotes
- When AlphaZero’s first unofficial match games were released (2017), several positions displayed an evaluation label “Undefined” in DeepMind’s internal viewer because AlphaZero does not calculate numeric scores in the traditional sense.
- In some old Soviet chess magazines, game fragments would be annotated “Неопределено” (“undefined”) when the analyst invited readers to continue the investigation at home.
- The term occasionally pops up humorously online—e.g., “GM X has perfected the Undefined Defense; no one knows what he’ll play until the clock starts.”
Summary
While undefined is not a classical chess term with fixed content like en passant or castling, the word nevertheless appears in modern chess discourse whenever a position, result, or evaluation has not yet been determined. Recognizing such moments—whether you are writing an engine interface, directing a tournament, or composing a problem—will help you communicate clearly and avoid confusion.