What does the word "Yin" in Mujiangyin mean?

Twilight: a poem written by the river at dusk. Yin, an ancient poetic style.

original work

The hymn of Twilight River

(Tang) Bai Juyi

Sunset spreads in the water,

Half the river rustles and half the river is red.

Poor night of September 3rd,

Dew is like a real pearl, and the moon is like a bow.