"Bum" is used in England, in the US we don't use this much. "Bottom" or "booty" is usually used with young children but older kids and adults say "butt".

I mean you posted in an area where the readers read English. "For learning · English / Written in · English / Category · Culture" Seems it worked, but if you posted instead in "Written in Portuguese" you'd get more who could actually read the Portuguese. Unless these guys read Portuguese, they are guessing what "bumbum" means. If they guessed correctly, it worked. :)

Nanren, I've just started to study English. So, I wasn't sure if what I had written in English was understandable. To ensure, I wrote in Portuguese too. Thaks for your answer!

You can say "bottom". I remember not being allowed to say "butt" as a young child even though it's just short for "buttocks", a word I don't think is heard much anymore.

Maybe post in Learning English, written in Portuguese?