Note: Do not add "鉛筆" (pencil) to translated tags. It's often misused on pixiv and leads to lots of mistags.
If you've ever used a pencil in your life, chances are it was a graphite one. Coming in all sorts of shapes, sizes, and hardnesses, this medium has been popular for centuries. Art on Danbooru using this medium will often be done with a 「シャープペン」, that is, a mechanical pencil, but the characteristic that sets pencils apart is the range of pleasing monochromatic values and shading techniques that can be employed with only subtle modulation of stroke and pressure.