A template or pattern is a possible configuration for all instances a single digit that does not violate the Sudoku rule. For a standard Sudoku, there are 9 instances in each template. Here is an example:
In a standard Sudoku, there are 46656 different templates. Additional constraints have a considerable effect on the number of available templates. For example, Sudoku-X has 25608 different templates. The example would be invalid for Sudoku-X.