What mean sodoko in Japanese?

The word "Sudoku" is actually not Japanese, but a shortened form of the phrase "Suuji wa dokushin ni kagiru" (数字は独身に限る) which translates to "The numbers must be single" or "Digits must be single" in English.

So, while Sudoku is a Japanese puzzle, the word itself is not actually a Japanese word. It's a phrase used in the game's instructions that was shortened and popularized as the name of the puzzle itself.