Hueco literally translates to "hole" or "empty space." While it can refer to a physical void, it's often used metaphorically to describe an emotional emptiness or a gap left by someone's absence.
In this song, the lyrics say, "Y encontrarás un hueco aquí, en mi corazón" (And you'll find a hole here, in my heart). It powerfully conveys the idea that the singer's heart, once full of love, will now have an empty space where the former lover used to be, symbolizing the emotional void left by their departure and the singer's moving on.
This T3r Elemento song, "¿Y Todo Para Que?" [And All For What?], is a powerful breakup anthem where the singer is completely over an ex. He's not holding back, telling his former love, "Si ya te perdí, pues que sea para siempre" [If I already lost you, then let it be forever]. He's done trying to make things work and is ready to move on, even if it means crying for a bit. He's confident that the tables will turn, and soon she'll be the one regretting everything.
He remembers all the effort he put in, trying to treat her like a queen: "Traté de darte el papel de princesa, comprándote lujos para que fueras mi reina" [I tried to give you the role of a princess, buying you luxuries so you would be my queen]. He was there for her through tough times, "Haciéndote fuerte cuando estabas triste" [Making you strong when you were sad]. But in the end, he realizes it was all for nothing because "Tú nunca me quisiste" [You never loved me]. He's moving on, declaring, "Ya no estaré para ti" [I won't be there for you anymore], and he's sure she'll eventually regret losing him.