It looks like lampcord. It could have been an extension cord for some device, although an outlet end would usually be left rather than cutting it off to a plain wire.
I could have been used to power outdoor lights. These often use lampcord as their feed. They are usually directly wired rahter than plugged into an outlet type connector. If they were removed, the wire may have been cut rather than more carefully removed.
The risk here is that, if it powered lights, it may be controlled by a switch. If so, the line is dead now, but could be repowered by turning that switch on.
Speakers are also usually powered by lampcord. This could have been an outdoor speaker and the wire was cut rather than disconnecting it when it was removed.
Checking with a tester is a good move. If you got no reading when the tester was held at the cut end probably means it is not hot (at least not line voltage hot).
Your best bet is to try to trace it back to a source. Get a sense of where it enters the building and see if there is any indication of it on the inside of the house. Also look for switches whose use is unknown.