Calderón literally translates to "cauldron" or "large pot." However, in the context of this song, it refers to the Estadio Vicente Calderón, the former home stadium of the Atlético Madrid football club.
The lyric "lloró el calderón en Madrid" (the Calderón cried in Madrid) is a poetic way to describe the emotional atmosphere and the collective tears of the fans at the stadium, likely during a significant or poignant moment for the team. It's an interesting word because it uses a common noun to evoke a specific, emotionally charged place, making it unique to this song's narrative.
Dani Martín wrote "Dieciocho" as a postcard to his own eighteen-year-old self, opening on the night his old band filled Atlético Madrid's stadium: "Tocamos el cielo en mi estadio, lloró el calderón en Madrid" [We touched the sky in my stadium, the Calderón cried in Madrid]. The song counts what survives once the years pass — "Nos queda una canción, nos queda la emoción" [We have a song left, we have the emotion left] — and anchors that memory in one small scene from childhood, his sister covering his eyes: "'Pequeño', mi hermana lo hizo por mí" ["Little one", my sister did it for me]. The same chorus opens and closes the song, so that one stadium night stands in for every "crazy year" that came after.