This is the 792nd most frequent Japanese word.
気分
Mood; feeling.
In this sentence, '気分' is used to express the speaker's mood or feeling.
今日は気分がいいです。
I feel good today.
Here, '気分' refers to the person's emotional state influenced by external factors.
その音楽を聞くと気分が落ち着きます。
Listening to that music calms my mood.
In this example, '気分' is part of the compound '気分屋', which describes a person whose mood frequently changes.