Träumerei noun (German)
dream [noun] a state of being completely occupied by one’s own thoughts
Don’t sit there in a dream!
reverie [noun] a state of pleasant dreamy thought
He was lost in reverie.
The piece be Robert Schumann is part of Kinderszenen Opus.15
The music for this, the piano solo and many other arrangements can be found on this link to the website IMSLP - Sheet music link
Practice Piano Accompaniment at 55 bpm