Translation:I do not know!
I sometimes watch Arab series and they generally say "ma baref" (I guess it would be "ما بعرف") when they don't know something. Can any native speaker explain the difference to me?
The sentence here (and what Duolingo is supposed to teach) is MSA (modern Standard Arabic) which is a continuation of the Classical Arabic.
The phrase you mentioned is a dialectical one (Levant style, i.e. Lebanon, Syria and surroundings).
This said, Duolingo does use lot of dialectical words in this course and we talked about it in the forum here but I don't think Duolingo is changing that any time soon. Example: using شنطة instead of حقيبة for "bag" (شنطة is originally Turkish: çanta).