The one in (by far) the most widespread use is the ATR. You can read about it here.
Other indicators that can be used to display the volatility of currency pairs include standard deviation, the Keltner Channel (based on an ATR-multiple distance from a specified MA), and Bollinger Bands (similar but based on standard deviation rather than on ATR, not as helpful in my opinion).
That’s something different.
It’s displaying the volatility of individual currencies, not of currency pairs (though it’s based on those).
According to the explanation given on the page you linked to, it does that by monitoring all 28 pairs formed by all the combinations of the 8 “majors” and then displaying for each individual currency some kind of “averaged out” figure reflecting how it compares, on average, with each of the other 7. The indicator(s) used to calculate it aren’t specified.