Preset
A saved set of settings with a name, one click back to a known look.
See it in Fractal mirror. Pick Escher spiral under Presets, then move a slider and pick it again to return.
In plain words
A tool can have dozens of sliders, and a good look may need many of them set just right. A preset stores all those settings under one name. One click loads the whole set. It is a quick way to start, and a safe way back after experimenting. Many presets are a good place to learn what each slider does.