One of my pet peeves about expressive, terse syntaxes like this is that the features are not Google-able. Entering {} or !#:1 or !? in the search bar is more like swearing than like learning. This one happens to be called "Brace Expansion".

https://www.gnu.org/software/bash/manual/html_node/Brace-Exp...

Importantly, realize it's a feature of Bash that deals with strings, not a feature of mv that deals with filenames. It just replaces a word containing a brace expression with a set of words that contain each pattern in the list.

In general, though, I wish that terminals and text editors that do nice things like syntax highlighting and autocomplete supported help text better. Perhaps selecting some text and hovering with your mouse or hitting F1 could bring up a minimal syntax example of the feature you're looking at...