Ambición translates to "ambition." It's an interesting word choice in a song about a breakup, as it often carries connotations of striving for success or power.
In "Bajo Cero," the artist uses it to reflect on a past relationship, singing, "no me acuerdo todos los que fue tu ambición" (I don't remember all that was your ambition). This suggests that perhaps the partner's ambitions played a role in their separation, or that the singer is trying to forget the driving forces behind their ex's actions. It adds a layer of depth beyond a simple love lost.
Kid Flex's "Bajo Cero" is a really honest look at trying to move on from a past relationship. He starts by admitting, "no creo que te pueda olvidar" [I don't think I can forget you], and misses simple things like walking together. It sounds like he's trying to process a lot, thinking about all the things he wants to share but can't because the person isn't there, which "me pone mal" [makes me feel bad].
Even though he wants to find them, he knows he can't, so he decides it's "mejor a bajo cero" [better below zero] if they're not together. This song is all about letting go, as he sings, "ahora me toca soltar y ahora me toca dejar" [now it's my turn to let go and now it's my turn to leave]. He's determined to keep moving forward with his own goals, even if he's hurting right now, believing "algún día va acaba de esto" [someday this will end]. He's also pretty blunt, saying "todo lo que tú dijiste mentí tras tu bebé" [everything you said was a lie behind your baby], and he just wants to forget the pain and ambition that hurt him.