When humans were at their peak as a society, both in terms of prosperity and in terms of society functioning.

[It's just chatter, to them; doing an entire lecture on the Radiant Era would take a lot more notes than V actually has. Normally they'd lean on Philo for a better recounting of the details, the ones that have survived, but none of their team is here anyhow.]

Yes, that's correct. It can also damage most people's skin, as the acid residue from it is corrosive.