A cuboid, also known as a rectangular prism, has 12 edges. However, diagonals are not considered edges, but rather line segments that connect non-adjacent vertices.

To determine the number of diagonals in a cuboid, we can use the formula:

Number of diagonals = (n * (n - 3)) / 2

Where n represents the number of vertices in the cuboid.

A cuboid has 8 vertices, so we can substitute n = 8 into the formula:

Number of diagonals = (8 * (8 - 3)) / 2
= (8 * 5) / 2
= 40 / 2
= 20

Therefore, a cuboid has 20 diagonals.