The meaning of icons of different functions.

Hello, everyone.
I have some question about the Icons in the upper left corner of some functions. Like the screenshot I attached, are there any differences between functions with these three different Icons, or what do these Icons imply?

According to my research, the first Icon like an arrow means that this function is used to call events elsewhere.
The second square icon is my most confused one. Is it used as the interface for input and output of custom function or wrapped nodes? I saw people call this tunnel in some places
But why do nodes such as the “Async load asset” have such icons when they are not wrapped?