Automatically generated backup file created by Blender, an open source 3D modeling application; stores a backup copy of a .BLEND document from the past save operation two saves ago; contains the saved version prior to the .BLEND1 backup file, which is the immediate backup version of the BLEND document.
Blender will make as many backup copies of the BLEND document as specified in the user application preferences. Therefore, you may see ".blend1," ".blend2," ".blend3," etc. files alongside your current ".blend" file for as many times as you use the application save operation.
To restore a BLEND2 file to a Blender document, rename the file extension from ".blend2" to ".blend" and open it normally.