The medium commonly used for charcoal drawing is charcoal sticks. Charcoal sticks are made by heating wood (typically willow or vine) in an oxygen-restricted environment until the organic material converts to carbon. The resulting sticks are soft, dark, and easily applied to paper, making them ideal for expressive, tonal drawing.
Charcoal drawing is named after its medium, so the answer is self-evident: charcoal sticks are the defining material of charcoal drawing. They come in several forms, including vine charcoal (thin, delicate sticks), compressed charcoal (denser and darker), and charcoal pencils (charcoal encased in wood for finer control).
Graphite is the medium used in pencil drawing and produces a shinier, lighter mark than charcoal. Oil paint is a painting medium, not a drawing medium. Ink is used in pen-and-ink or brush drawing, which is a distinct technique from charcoal drawing. Each of these media produces results with different qualities of line, tone, and texture.