Data silos can occur in companies, in municipalities, even on a larger scale (national). We speak of a data silo when data is stored at various locations in an organization and only certain organizational areas have access to this data, but there is no networking of these locations and areas.
In agriculture, the term "silo" refers to closed containers in which, for example, grain is fermented in isolation from the rest of the organization.
Data silos are problematic because they lead to inefficient, resource-intensive parallel structures instead of linking data in a meaningful way. "Data silos, the biggest risk of digitization" (DKSR website). But also in municipalities, "Life in cities is networked. Data is not."
Urban data platforms help to break down data silos as they enable access to and linking of data.