Barks
Also said as Ambient dialogue, Reactive dialogue, Dynamic dialogue
Short lines characters say by themselves in response to what is happening: "Reloading!", "That was close." The trigger comes from game state, not from a script.
Barks make the world feel as if it is paying attention, for very little writing per line. If they repeat, they become the most annoying thing in the game, so they need cooldowns and memory.
Say it
“Add companion barks fired from state: low health, a second hit within 5 seconds, a coin found. Choose the most specific rule, wait at least 8 seconds between barks, and never play a line twice in a row.”
Where you’ve seen it
Left 4 Dead matches hundreds of world facts against thousands of lines and picks the most specific rule that fits, as Valve's Elan Ruskin explained at GDC in 2012. Hades has about 21,000 voice lines, so characters rarely repeat themselves.
Not to be confused with cutscene
A cutscene plays once at a planned time. A bark can fire at any moment, again and again, so it must make sense wherever the player happens to be.