Musical Session is a minigame featured in Ocarina of Time.
Found right from the first room of Lost Woods, in the same area where a Deku Scrub runs its target game, are two Skull Kids, holding one flute each. When Link stands in a wooden podium before them, he can show his Ocarina to start the minigame.
One Skull Kid plays three notes with its flute, the second Skull Kid imitates the tune, and then Link does the same. When he succeeds, one Skull Kid extends the tune by one note, the other imitates that extended tune, Link does the same, and the process continues until the two Skull Kids congratulate Link for following them correctly, and give him a prize.
Each session starts with a tune played with up to three notes, but each ongoing session will consist of longer tunes. The first session has a tune extended to five notes, the second session has one extended to six, and the third section has one extended to eight; the tunes themselves are random, so Link must pay attention to each incoming new note. Also, if the young hero makes a mistake just once in a session, he will have to restart it with a new tune.