Holgazán translates to "lazy person" or "idler." It's a colorful and somewhat old-fashioned word that isn't heard in everyday conversation as often as more common synonyms.
In the song, the narrator describes himself as "Y yo, que hasta ayer solo fui un holgazán" (And I, who until yesterday was just an idler). This word choice immediately sets up a transformation, highlighting how the love interest has changed him from someone aimless into the "guardian of her dreams of love," making it a memorable and impactful word in the context of the lyrics.
Jarabe de Palo, with Alejandro Sanz, gives us a beautiful song about being completely swept away by love. The singer starts by admitting he was a "holgazán" [lazy person] until yesterday, but now he's the "guardián de sus sueños de amor" [guardian of her dreams of love]. He loves her so much, he says, "La quiero a morir" [I love her to death].
This woman sounds incredible! She can "borra las horas de cada reloj" [erase the hours from every clock] and even "enseña a pintar transparente el dolor" [teaches me to paint pain transparent]. She builds towers from the sky and gives him wings to fly. He feels totally captivated, like he's caught in a "lazo que no aprieta jamás" [a knot that never tightens], a silk thread he can't and doesn't want to let go of. It's a song about being utterly devoted and transformed by someone you love deeply.