Swotch Channels question

[RandyT]

In the Switch Channels panel, there an option called 'Function'.
It is a drop-down pick-list.
As we would expect, there are many functions listed. For example, Thunderstorm.
It also shows Thunder as a function. I haven't found this as a defined event or process in other panels.
What is Thunder, and how would it typically be used? What comes to mind is some kind of audio device, but that is just guessing.