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A letter A to E followed by two digits.
Also known as: Encyclopaedia of Chess Openings code, Opening code, B90, Chess opening classification
An ECO code identifies a chess opening by a letter and two digits — B90 is the Najdorf Sicilian. It classifies by resulting position rather than by move order, so two different sequences reaching the same position share a code.
Denotes a chess opening classification code from the Encyclopaedia of Chess Openings: a letter from A to E followed by two digits.
Contexts: History
Classifies by the position reached rather than by the sequence of moves, so transpositions to the same position carry the same code.
Contexts: History
Divides the whole opening repertory into five volumes by first move and structure, which is what the letter encodes.
Contexts: History
Is a publisher's classification rather than a governing-body standard, though it is used universally in databases and literature.
Contexts: History
A single capital letter from A to E followed immediately by two digits, printed beside an opening's name.