Diagonally means moving or positioned at a slant, cutting across from one corner toward an opposite corner rather than going straight along an edge. If you walk diagonally across a rectangular playground, you're taking a shortcut from one corner to the opposite corner instead of walking along two sides.

Think about a square: you could trace your finger along the top edge and then down the right edge, or you could cut directly across from the top-left corner to the bottom-right corner. That slanted line going corner-to-corner is diagonal.

In checkers, pieces move diagonally across the board, stepping from one colored square to a touching square of the same color. When you cut a sandwich diagonally, you slice from one corner to the opposite corner, creating two triangular halves. A bishop in chess can only move diagonally across the board, traveling along those slanted paths rather than moving in straight lines like a rook.

Anything diagonal forms a slant or angle rather than running perfectly horizontal (side to side) or vertical (up and down). In a rectangle or square, a diagonal line between two opposite corners is the shortest path between those corners.