What does it mean?
Spread changes the side signal: 0 moves toward mono, 1 preserves width, and 2 widens it. It does not create stereo from an identical mono input.
ExampleWiden after a stereo chorus or delay, then test the mono fold-down.
How the meaning changes between controls
Stereo Width
The amount of the Side component on a 0–200% scale: 100% preserves stereo width and 0% makes it mono.
Reverb
The stereo spread of reverb ambience, displayed on a 0–100% scale.