I'm pretty embarrassed to admit I don't know this one...I just realized I've always just described it, not actually named it :)
So, that folder/directory collapse/expand symbol thingy, you know, this one:
What is it called?
Some file managers depict it as a plus/minus sign, others as a triangle with changing orientation and/or color, and other file managers have yet different symbols for it.
But I'm looking for the generic name of the functionality.
My Google searches have so far all resulted in "plus/minus symbol" or "folder tree triangle" or similar, all referring to the specific icon or symbol used to represent the functionality (and, as usual, using the terms "folders" and "directories" interchangeably).
But there just has to be a proper name for it!