This is the 1378th most frequent Portuguese word.
nisso
"In that" or "in this" (used to refer to something previously mentioned).
Here, 'nisso' refers to 'in that', where 'isso' is a demonstrative pronoun that signifies a previously mentioned idea or situation.
Eu não acredito nisso.
I don't believe in that.
In this case, 'nisso' refers to 'in that idea', highlighting agreement in context related to the preceding discourse.
Nisso eu concordo com você.
In that, I agree with you.
In this usage, 'nisso' points to 'on that particular topic or issue', which was mentioned earlier in the discussion.