This is the 1367th most frequent Japanese word.
ピアノ
Piano.
In this sentence, 'ピアノ' (piano) is used as the direct object of the verb '練習しています' (practice). It refers to the musical instrument that is being practiced.
私は毎日ピアノを練習しています。
I practice piano every day.
Here, 'ピアノ' is used as the subject of the sentence, identifying it as the instrument that holds a preference for the speaker.
ピアノは私の好きな楽器です。
The piano is my favorite musical instrument.
In this sentence, 'ピアノ' is part of a noun phrase '大きなピアノ' (large piano), describing the presence of this item at a location.