A .blend file is the native file format used by Blender, a free and open-source 3D creation suite. It stores all the data necessary for a Blender project, including 3D models, textures, materials, animations, scenes, lighting, camera settings, scripting information (Python scripts), and user interface layouts. The .blend format is designed to be comprehensive and self-contained, allowing users to save and share their entire project in a single file. It supports various compression methods to reduce file size without significant data loss. Because it's a complex binary format, it's not easily editable with standard text editors. The format is constantly evolving with new versions of Blender to support new features and improvements. Opening a .blend file in an older version of Blender might result in compatibility issues or data loss. The .blend format is crucial for artists, animators, game developers, and anyone working with 3D content creation using Blender.