As far as i remember, it isn’t mentioned in the first 7 books. It might be mentioned in the curse we don’t like to talk about (the cursed child) and/or in all her ramblings on pottermore or whatever that site was called.

Uh and they have some really nice looking pants, so I definitely have to consider them.

My most outdoorsy friend also mentioned them. So I think I’ll try a few local shops tomorrow and if i don’t find anything i like, I’ll give Revolution Race a try. I just hate buying clothes online.