The stump is a tool to assist in the shading of a drawing but we can also use the stump in our application of dry media like charcoal, Conté or graphite.
The stump comes in a variety of sizes and is basically a solid cylinder, usually made of compacted paper. It's pointed at both ends and ideally we keep one end clean, for the light removal of applied media, and one end dirty, for smudging and shading.
We can also sketch with the stump tool, pretty effectively, by using powdered charcoal (can be bought or produced easily with sandpaper). The feeling is closer to painting but with the flexibility of dry media, as we're able to almost endlessly apply and remove using an eraser.
The stump is great for softening lines and edges. So, if you want your drawings to have a rich combination of hard and soft edges, you can use this tool to help achieve that effect.
We can lay in our darks and then use the stump tool to create midtones with controlled smudging and wiping. We get really accurate by using the sharp tip or make broad economical strokes by tilting the tool.