The structure and encoding used to store or transmit data, such as CSV, JSON, XML, GeoJSON, or Shapefile.
Choosing the right data format depends on the use case: CSV for simple tabular data, JSON for hierarchical or web data, GeoJSON for geographic web data, Shapefile for GIS desktop data, Parquet for large-scale analytics. Open, standard formats are preferred for open data because they can be opened by many tools without special software.