The solution to the preceding puzzle is a Latin square. The pictures on the left are Latin squares. You've probably noticed that they share something similar. In the 3 by 3 grid, each cell contains one of 3 different tokens - red, blue, or yellow. Each row and each column contains all three types of tokens.
In the 4 by 4 grid, each cell contains one of 4 different symbols. Each row and each column contains all four different symbols. There are also 5 by 5 Latin squares, 6 by 6 Latin squares, and so on. A typical Sudoku puzzle is a special type of a 9 by 9 Latin square.
There are other puzzles also based on Latin squares. Here are a few. They are inspired by puzzles from the World Championship of Puzzles.