I can take a stab but I thing Rachylou is right, and I don't trust anyone to use terminology correctly.
" Business formal" is supposed to mean a category of business wear, not " formal attire" so it's the matching suit look, very polished-- pantsuit or skirt suit would depend on your environmental norm, either one if not otherwise dictated. The business person would know or learn what that is-- daily wear in some businesses, the lawyer going to court, the meeting with the boss or special client.
For your charity event, you also need more info. Usually the event promotion tells guests what attire. If you are a sponsor or otherwise at the podium, you'd probably be dressed at the higher level of expectations. If it's a " Gala" and " black tie" or " formal attire" or even black tie optional, you'd likely want to wear a long gown rather than a cocktail dress. That would be in the spirt of the event. However if the event has a long history, you might seek some advice on what folks in your situation have done. Some charity events are on weekday nights and it's expected for people to come straight from work. Then you would be in street length dress or sharp pants outfit and a little dressy, kind of "day- to - evening" look, because charity events have that vibe of " trying", not just schlumping along.
I'm sure others will weigh in. Information is key since events often have their own " personalities".