What's the Category List?

[spencered]

There are lots of references to it and no definition of it.

[pianoleo]

See the second numbered definition here, for instance: Engraving Options dialog

[Lillie_Harris]

Or as discussed in a thread a few hours before yours

Roman numerals in parts

If you’re ever not sure about this sort of thing, you should find it described/labelled on the page for the corresponding area or dialog, e.g. here for Engraving Options.