It’s one of the engineering terms generated by what real-world thing closely resembles what we’re doing. Video noise is called “grass,” Loud sound distortion is called “clipping” from what the blue waves look like.
If you run Effect > Equalizer and tell it to do nothing, it will have a flat, straight, blue/green horizontal line starting on the left at 0dB. No curve.
If you need the tool to do some work, to boost some musical tones and suppress others, then that blue/green line won’t be flat any more. It will have a curve or bend to it.
Different curves will have different affects. That gives us the engineering shortcut: “I’m running the equalizer tool now, which curve should I use?”
Low Rolloff for Speech is a custom curve designed for voice work. It started out life with everybody designing their own curve. Steve designed this one with my historical notes to do the most good and still cause the least sound quality damage. It became a standard tool in Audacity 2.1.3.
Read the notes on this page.
https://forum.audacityteam.org/t/audiobook-mastering-subaudible-noise/45764/9
I go on forever what it does and why you need it.
Koz