A cuboid has 6 rectangular faces.

Explanation:
A cuboid is a three-dimensional shape that has six rectangular faces. These faces are arranged in pairs of three, and each face is a rectangle.

- Definition of a Cuboid:
A cuboid is a solid figure that has six rectangular faces, eight vertices, and twelve edges. It is also known as a rectangular prism.

- Characteristics of a Cuboid:
1. Rectangular Faces: A cuboid has six rectangular faces, where each face is a parallelogram with four right angles.
2. Edges: A cuboid has twelve edges, which are the line segments formed by the intersection of the rectangular faces.
3. Vertices: A cuboid has eight vertices, which are the points where three edges meet.

- Visual Representation:
To visualize a cuboid, imagine a rectangular box or a brick. The top and bottom faces are rectangles, and the sides are also rectangles. The front and back faces are also rectangles. All these rectangular faces together form a cuboid.

- Number of Faces:
Since a cuboid has six rectangular faces, the correct answer is option 'C' - 6.

- Example:
Consider a cuboid with dimensions: length = 5 cm, width = 3 cm, and height = 4 cm. In this case, the top and bottom faces will have dimensions of 5 cm x 3 cm, the front and back faces will have dimensions of 5 cm x 4 cm, and the side faces will have dimensions of 3 cm x 4 cm. All these faces are rectangles, resulting in a total of six rectangular faces.

Therefore, a cuboid has six rectangular faces.