what is blend1 file?

Alot of times when I save a blender file lets say its something like monkey.blend I will notice later that it will also save another file of the same name titled monkey.blend1 what is this blend1 file and why does blender save it?

Thanks

it is a baclup file for the main file
so if the main file get srcewed up then you have a backup you can use
but before you have to change the name to blend to reuse it

That;s all

Salutations