Depends... But if you mean in case of productivity, I would say it is
the 'Current', Ampere.
yes, even in empty space
(e.g. Pulsar strikes, ~100 Tesla strong...
you could foist a whole soccer-stadium with a superstrong Ring onto
such a Pulsar strike, which strikes into empty Space without having a
massive conductor, just the Space which surrounds a Pulsar)
It is said a copper conductor can be informed, similar to water, that
they have a direction after some time of usage. (I never heard that!)
Also when the surface of the conductor is becoming rusty, you will
loose high frequencies (e.g. Hi-Fi), bass and deeper sounds are more in
the core of the conductor. (Tis is easy to hear! A very important part
of any sound-setup, I do need with any kind of Audio work... I prefer
'wires' in any case. Lace-wires only when it doesn't work other.
back and forth. Yes, with AC. But even there is an attracted movement
to a direction, indeed.
It depends how you inform a piece of 'whatever'...
Preferably something metal... precious metals.
But we would go to Magic now....
No, AFAIK nobody can tell what electricity is. Only the effects are
well known and calculable. A potential dividing and multiplying force,
mathematically right... as seen with many forces of the Universe, IMHO.