What is a Pencil?

          A pencil is an instrument used for writing or drawing, consisting of a thin stick of graphite or a similar substance enclosed in a long thin piece of wood or fixed in a cylindrical case.

          Most pencil cores are made of graphite mixed with a clay binder which leaves grey or black marks that can be easily erased. Graphite pencils are used for both writing and drawing and result in durable markings. Colored pencils are typically regarded as art supplies. Grease pencils have a softer, crayon-like waxy core that can leave marks on smooth surfaces such as glass or porcelain. The most common type of pencil casing is of thin wood, usually hexagonal in section but sometimes cylindrical, permanently bonded to the core. Other types of pencil core are less widely used, such as charcoal pencils, which are mainly used by artists for drawing and sketching.

References:

https://en.oxforddictionaries.com/definition/pencil

https://en.wikipedia.org/wiki/Pencil