Diagonal is a line that connects two corners of a shape that aren't next to each other, cutting across the middle rather than following the edges. In a square, you can draw two diagonals: one from the top left corner to the bottom right, and another from the top right to the bottom left. These lines cross each other right in the center, dividing the square into four triangles.

You can spot diagonals everywhere. When you walk straight across a rectangular field instead of following the edges, you're taking the diagonal path. It's the shortest route between opposite corners. In checkers, pieces move diagonally across the board. When you cut a sandwich from one corner to the opposite corner, you're making a diagonal slice.

The word also describes anything slanted or tilted. A diagonal stripe on a shirt runs at an angle rather than straight across. Diagonal lines can feel more dynamic and interesting than straight horizontal or vertical ones, which is why artists and designers use them to create energy and movement in their work.