In Romanian "carapace" means shell. It seems to mean the same in English, too, but I presume is seldom used: https://en.wikipedia.org/wiki/Carapace

It's the biggest solid piece of shell in English. Like the stuff over a crabs pincers is still shell but only the stuff that surrounds the main body is the carapace. Often used as an analogy for other sorts of armor, like a knights breastplate being his carapace or a tank's hull armor.

It's not uncommon in English, though I suspect it's most often used in technical fields like entomology.

I'm pretty sure you encounter in in science fiction as well, where some bug like alien has a carapace or a soldier has some armored exo-skeleton described by the word. Though I cannot think of any specific examples.

Quite common in videogames, too.

A specific example would be the Carapace (armor) upgrades in Starcraft 2 (one faction, the Zerg, are basically insects).

Also sometimes used for (humanoid) armor crafted from shells (fantasy settings).

I think this is MUCH more prevalent in scifi/fantasy targeted at male audiences, and the data confirms it [1]

[1]: https://osf.io/g4xrt/#!

The Dota 2 hero Nyx Assassin (beetle-like creature) has a skill called Spiked Carapace.

It's pretty commonly used in my experience, but that might just be the types of books I read perhaps.

Carapace is rarely used outside a zoological context, but people may be more familiar with the derived word "scarab", being a beetle with a notable shell. It is unfortunately unrelated to the delicious dish carpaccio, which is named after a man.

I suspected Brandon Sanderson made it up for his Mistborn series until hearing it in Project Hail Mary also. This is actually why I clicked the thread: was curious if anyone would make the reference!