Unity Assets 3D models are pre-made, optimized 3D assets (e.g., characters, props) from the Unity Asset Store, while Unity 3D models refer to any 3D model created or used in the Unity engine.
Unity Assets 3D models are ready-to-integrate—built for Unity’s workflow to save development time. Unity 3D models, by contrast, can be custom-made (in tools like Blender) or imported from other sources, as long as they’re compatible with Unity.
For quick Unity project prototyping, using Unity Assets 3D models from the Asset Store is a practical way to avoid building everything from scratch.