An element of T is called a tile . The checkerboard is an example of a periodic monohedral tiling. In the brick wall the collection T consists of the rectangular faces of the bricks. Each face is a tile. Each hexagon in the beehive is a tile.
T is the collection of all the squares.
Each piece of dried mud in the flat is a tile and T comprises all of the pieces. For example, these three tiles are all congruent to each other. Conversely, these two tiles are not congruent because they are not the same shape. Similarly, these two tiles are not congruent because they are not the same size. Let P be subset of T such that each no two tiles in P are congruent.