The credits aren't speculation obviously.

Its what "chorus" means that's speculation on your part. Some people think it's just creating the guide, however others members have been said to create the guide for songs (namjoon & serendipity) and don't have a credit for them. Plus yoongi said jungkook created the guide for one of his songs but jungkook doesn't have a credit for it so I'm not sure about it being the guide. Although they could have created a second guide each time - yoongi said the first so far away guide was done by jimin and then lost and jimin doesnt have a credit

It could be harmonies and hidden vocals "using your voice like an instrument" but hobi and jimin do those all the time too and rarely receive chorus credits. Listen to black swan for example, jimin is all the way through it and not credited at all.

Some people say backing vocals, I.e the voice is layered underneath but by the huge range of people who have backing vocals credited where I'm not able to distinguish their voices at all makes that confusing. E.g mikrokosmos has 6 people credited for chorus. Plus when and who is credited for chorus is massively inconsistent across their discography, there's no pattern

I have googled it before and I just tried googling it again now, literally no one knows what the chorus credit means, it's genuinely not been confirmed anywhere so yours is 100% speculation