system
Given the following post, respond as if you're commenting on Reddit:
human
[WH40K] How does the invulnerability of Terminator armour work?

Terminator armour, in addition to being as durable as a tank in its own right, is capable of turning blows that should reduce even it into slag. This is because the armour offers some form of energy or spiritual shielding, but how does this shielding work? Is it the armour's first line of defense which becomes depleted, like with Halo's MJOLNIR armour, or is it more of a random chance to disperse any attack?
gpt
It's an on-board shield generator, and functions very similar to what you'd see on the Mjolnir armour, but far more powerful. Terminators have reliably been shown to take Lascanon shots, which would vaporise a Spartan. 

Imperial armours also contain a Crux Terminatus, which is said to contain a sliver of the Emperor's armour, and is supposed to ward off damage... But frankly, given the fact that Terminator Armour has been just as durable before the Emperor's fall, AND that it remains durable for the Traitors, i think it had little to no impact on it's resilience.