Final answer:
The flow setting determines the amount of paint sprayed by the airbrush tool in graphic design software, affecting the opacity and intensity of the color applied.
Step-by-step explanation:
When using the airbrush effect in graphic design software, the flow setting is what determines the amount of paint that is sprayed while the mouse button is held down. The flow setting regulates how much color is applied to the canvas with each pass of the airbrush tool. A lower flow setting would result in a lighter, more transparent spray of paint, while a higher flow setting would give a more opaque and intense color application. Adjusting the flow rate allows artists to control the intensity and coverage of the airbrush effect, enabling them to achieve the desired effect on their digital artwork.