A silo is an enclosure or bin for the storage of large quantities of some commodity, such as oil or grain. It can take the form of a large tank or a storage shaft, and its shape can be cylindrical, rectangular, hemispherical, spherical, or very often a succession of joined cylinders.

The enclosure holds the commodity in bulk. The stated contents include liquids as well as particulate solids, so the form is not limited to grain storage.

Its shape can be a single container or a succession of joined cylinders. Storage purpose and enclosure form remain separate from the particular commodity inside.