Reverb
Also said as Reverberation, Room sound, Convolution reverb
The thousands of echoes that follow a sound as it bounces around a space, blurred into a tail. Its length and colour tell your ears the size and material of the room.
It places a sound in a space, even with your eyes shut. Dry sound in a cathedral looks wrong without anyone being able to say why. Too much turns everything to soup.
Say it
“The hall needs about 1.8 s of reverb, the closet about 0.3 s. Send footsteps and voices to it at 25%, and keep gunfire drier so it stays punchy.”
Where you’ve seen it
Forza Horizon 5 was reported to use ray tracing for audio, which Playground Games compared to echolocation. Microsoft's Project Acoustics takes another route, simulating sound waves through a level ahead of time and handing designers the results as reverb settings.
Not to be confused with echo
An echo is a distinct repeat you can pick out. Reverb is so many reflections so close together that you hear one smooth fade.