Minecraft wiki entry for Custom_world_generation, associated text: Structure features are a special type of feature that generates a structure. Configured structure features are stored as JSON files within a data pack in the path data/<namespace>/worldgen/configured_structure_feature. The logic behind what qualifies as a structure feature versus a regular feature is unclear. Dungeons and Desert wells are typically considered structures, but are not structure features. Also, Nether Fossils are structure features while Fossils are not even though they are essentially the same feature.