This is the 12588th most frequent Polish word.
nastroju
"Atmosphere" or "mood."
Here, 'nastroju' is used to refer to the emotional state or mood of a person, specifically describing it as 'good'.
Jestem dziś w dobrym nastroju.
I am in a good mood today.
In this sentence, 'nastroju' describes the type of mood one is in during an activity, implying a bad mood.
Nie powinniśmy rozmawiać w złym nastroju.
We shouldn't talk in a bad mood.
Here, 'nastrój' (the nominative form) is influenced or affected by external factors like music, representing a general state of feeling in humans.