Llanto translates to "weeping" or "crying". While "llorar" (to cry) is common, "llanto" as a noun for the act of crying itself is a more evocative and slightly less common word.
In this song, the lyrics repeatedly mention "solo queda llanto y dolor" (only weeping and pain remain), emphasizing the deep sorrow and despair the singer feels. It's a powerful word that immediately conveys the emotional intensity of the song.
Armonia 10's "Mátame Mi Pena" is a passionate plea from someone desperate for their love to return. The singer is in deep pain, feeling like they can't go on without their partner. They repeatedly beg, "Vuelve mi amor" [Come back, my love], because without them, there's "Solo queda llanto y dolor" [Only tears and pain].
The lyrics really emphasize how much this separation is hurting them, saying, "Te matan esta pena te pido por dios ya no soporto este dolor" [This pain is killing me, I ask you for God's sake, I can't stand this pain anymore]. They feel like the days are just passing in a crisis, unable to resist or live without their beloved, making it clear this isn't just sadness, but an unbearable agony.