Plumas translates to "feathers". It's a beautifully poetic word that you don't often find in song lyrics, making it quite unique.
In this song, Alvaro Soler creates a surreal and romantic image, singing "Tus plumas bajo la luna, preguntan por mi" (Your feathers under the moon ask for me). The feathers, perhaps left behind on a pillow, are personified, symbolizing the lingering memory of a loved one who is now far away.
This song is a classic breakup anthem, but with a really hopeful twist. Alvaro Soler starts off feeling completely lost after a relationship has ended. He's afraid of the quiet, saying, "Le tengo miedo al silencio" [I'm afraid of the silence], and feels like he has nowhere to go now that this person is gone. He admits that even though the breakup might be for the best, it still hurts a lot.
The heart of the song is in the chorus, where he apologizes for the pain caused. He reveals he had all these beautiful words and songs saved up, singing, "Guardaba tantos versos / Sólo para ti" [I was saving so many verses / Only for you]. Now, he feels like he's just "canto al viento" [singing to the wind]. But what's great is that he doesn't stay sad. He recognizes that they weren't the "mejor versión" [best version] of themselves together and looks forward to a better future, knowing that "algún día parará de llover" [someday the rain will stop].