Well it means the system tries the best it can do make the value durable. It will do a sync after every write perhaps. If the disk lies, well there is not much sqlite can do. If disk has a capacitor and battery maybe it can still lie that it wrote but keeps it in its internal buffer and if someone pulls the cord it has enough energy to flush everything it "lied about" to disk. Oh but what if you shoot a proton beam through it and blow away its capacitor and battery, well then you are out of luck.

As someone mentioned, this is contrast to say how MongoDB was shipping not too long ago. They had turned of any acknowledgement for writes. So doing a db write was more like a throw over the fence and pray operation. So it didn't even try to be durable, by design.