What does it mean?
Delay feedback repeats echoes; flanger and phaser feedback strengthen resonances. Acoustic feedback is a physical speaker-to-instrument or microphone loop. These are different uses of the term.
ExampleMore delay Feedback produces more repeats, rather than simply making the first repeat louder.
How the meaning changes between controls
Delay
The portion of a repeat returned to create the next repeat.
Flanger
Feedback around a short delay; negative values invert the loop's polarity.
Phaser
Feedback that emphasizes the moving phase and notch response.
Acoustic guitar
A physical loop between a speaker and pickup or microphone that can cause howling.