What shape is unshaped pencil?

Pencils are cut from wood blocks and are originally either square or (less commonly) round. They are either smoothed to a ROUND shape, or milled to a HEXAGON (6-sided) shape, which reduces their tendency to roll away on a mildly slanted surface. (Thicker carpenter's pencils are oval for this reason.)

Pencils made from synthetic materials (plastic, polymer) can be extruded in any shape.