Salta means "jumps" or "leaps." While it's a common verb, its use here is particularly striking and poetic.
In the song, Paulinho Moska sings, "Minha lágrima salta" (My tear jumps/leaps). Instead of simply saying a tear falls or rolls, the word salta evokes a sudden, forceful, and almost involuntary release of emotion, making the image of the tear much more vivid and impactful. It captures the intensity of his sadness.
Paulinho Moska sings about a relationship that ended quietly, almost without either person noticing. He opens on a single word, 'Fim' ['End'], then works backward to how it got there: 'Porque um vazio foi se construindo em nós' ['Because a void was building in us'], 'Ficou distante pra escutar alguma voz' ['It became distant to hear any voice']. By the end, 'fomos desaparecendo sem ninguém desconfiar' ['we were disappearing without anyone suspecting'] it was already over.
Now on his own, he keeps running into her in ordinary moments: writing a new song, checking the mirror, 'Aqui no espelho eu me vejo sem você' ['Here in the mirror I see myself without you']. Instead of naming what he feels, the chorus gives one small, physical image and repeats it until it sticks: 'Minha lágrima salta' ['My tear jumps'], timed to the exact moment 'uma nuvem que começa a chover' ['a cloud starts to rain'].