Does the icon of arrows shaped as triangles pointing up and down have a name and what does it mean? I'm not sure if I can use it.
This icon seems to have different meaning in different systems:
- it's called "caret sort" or "chevron sort" in Carbon Design System;
- it's called "unfold more" in Material Design, while for sorting they use different icons;
- it's called "sort" in Font Awesome;
- Fluent Design System uses different kind of arrows for sorting, while the icon you provided, probably, doesn't have a set meaning for Windows users;
- the icon you provided is used in "Pop-Up Buttons" on macOS, so using it for sorting could be a problem for macOS users - some users could expect it to open a pop-up/drop-down when pressing it;
To answer your question - you have to consider if your users understand the icon: Do they come from the environment where the icon means what you want it to mean in your app? Is the icon used consistently in your app?
I'd recommend going with it and perform proper user testing when it's up.
It is one representation of a sort icon. When used next to a table header label, the user can sort in one direction by clicking once, and the other direction by clicking a second time.
I have seen some dropdowns on the web styled with the double arrows.
Also, in table headers it is used as a sort icon (fa-sort in font-awesome). So I guess you can use it for both.