Different ways to make an object ------------------------------------
There are only so many ways to make an object O. You can start with a larger block and gradually remove material until you have O. This is how sculptors work, starting, for example, with a block of marble. A great deal of material is wasted in this particularly resource-intensive process.
Alternatively, one can place exactly the right amount of material where it is needed. This is the principle behind casting: a metal is heated until it becomes liquid, then a mold is filled with the molten material. A part made in this way cannot always be used as-is and often needs further work. However, the amount of excess material is almost always negligible.
A blacksmith softens metal by heating it, then, while it remains soft, forces it into the desired shape.
3D printing reimagines these approaches, depositing material only where it is needed. It encompasses a variety of processes, such as fused-filament fabrication and stereolithography. It can use a wide range of materials: plastics, metals, resins, foodstuffs, and even living cells or concrete. But the basic idea remains the same.