Sudoku, for one, is a type of logic-based number puzzle game. It consists of a 9x9 grid with some of the squares filled in with numbers. The objective is to fill in the remaining squares with the numbers 1-9 in such a way that each row, column, and 3x3 box contains all the numbers from 1-9. The answer to the crossword clue FAD (3 letters) is 'CRAZE', as Sudoku has become a popular CRAZE around the world.