The name Sudoku is the Japanese abbreviation of a longer phrase meaning "the digits must remain single"; it is a trademark of puzzle publisher Nikoli Co. Ltd in Japan. Other Japanese publishers refer to the puzzle as Nanpure (Number Place), which was its original title. In Japanese, the word is pronounced [s??dok?]; in English, it is usually spoken with an Anglicised pronunciation (suh-DOE-coo or SOO-doe-coo).

The numerals in Sudoku puzzles are used for convenience; arithmetic relationships between numerals are absolutely irrelevant. Any set of distinct symbols will do; letters, shapes, or colours may be used without altering the rules (Penny Press' Scramblets and Knight Features Syndicate's Sudoku Word both use letters).

The attraction of the puzzle is that the completion rules are simple, yet the line of reasoning required to reach the completion may be difficult. Sudoku is recommended by some teachers as an exercise in logical reasoning. The level of difficulty of the puzzles can be selected to suit the audience.