I can't really describe it different other than fuzzy or soft...
This brush is to make fireflies in an illustration. I have some instructions on the picture below. If you want to add more color, just use the airbrush on layer mode "Overlay" in a warm yellow/orange color to brush on some more glow. Use the "Blur" brush over the glow layer(s) to give it the actual sight effect. Sometimes I use a more orangeish yellow, and other times I use a more green yellow, depending on the atmosphere of the illustration.
Hope this makes stuff easier! Thank you ♥

