.blend

3D image or animation project created with Blender, an open source 3D modeling program; contains 3D mesh data, lighting information, vertex painting, animation keyframes, NURBS objects, procedural textures, uvmapping layout, and realtime interactivity data; may also store multiple scenes in a single file.

BLEND files contain all objects, textures, sounds, images, effects, and scenes used in an animation. Therefore, a BLEND file is a project file rather than a basic 3D image or animation file.