AC or DC, it doesn’t matter. For current to flow you need two things:

   * voltage to ‘push’ it (potential difference)
   * a complete path for it to flow

A battery just sitting there without a connection is insulated. Touch *one* of its terminals and that terminal becomes the same voltage as you. But because it’s the same, no current flows.

Now touch the *second* terminal at the same time. A path is formed and current flows. That’s why you get a bit of a shock when you touch a 9V battery to your tongue, but only if you touch *both* terminals.

A power line has a reference to earth ground, at the utility from time to time on the poles, and at your home. If you touch it, and you are *also* grounded, current flows (ground, by definition, has almost no resistance.) If you are *insulated* from ground, perhaps by your shoes or by dangling in mid-air from a helicopter, (mostly) no current flows.

More here: https://electronics.stackexchange.com/questions/545322/professor-said-no-current-flows-to-ground/545334#545334

That said, there is still your body *capacitance* which provides an AC path. That’s why you can still get a shock from a live wire by touching just one terminal. It’s also the same way you can get a shock from static electricity.

And finally, a bit about ‘ground’. Earth ground used by utilities has a very small resistance, mostly in the element connecting to the earth itself. A grounding rod installed at a home has a specific standard it needs to meet: 25 ohms or less. Grounding systems for utilities will be much, much lower than that.

Early telegraph systems even relied on ground as a return, using only one wire to send a signal.