This is the 2419th most frequent Russian word.
песню
"Песню" is the accusative singular form of "песня," meaning "song" in English.
The word 'песню' (a song) is in the accusative case as the direct object of the verb 'исполнил' (performed).
Он исполнил песню на концерте.
He performed a song at the concert.
Here, 'песню' is in the accusative case as the direct object of the verb 'услышали' (heard).
Мы услышали новую песню по радио.
We heard a new song on the radio.
In this case, 'песню' is used in the accusative case as it refers to the song being recorded (direct object of 'записала').