Proceso literally means "process". But in this song, the phrase "la del proceso" is a modern, colloquial way of describing a serious, long-term partner.
It refers to the person you were 'in the process' of building a life with—your ride-or-die, the one who was with you through thick and thin. The singer deeply regrets leaving "la del proceso" for someone superficial, making this a unique and heartfelt term for a meaningful relationship.
Ever made a choice so bad that even your mom saw it coming? That is the exact regret driving "La Del Proceso" by Grupo Frontera and Manuel Turizo. The title refers to a popular Spanish phrase: "la del proceso" (the girl who stood by you through the struggle, back when you had nothing). The singer ruins his own life by leaving a genuine partner for someone shallow, admitting he got blinded by flashy looks. He bluntly confesses, "Cambié una de verdad por un maniquí" ("I swapped a real one for a mannequin") and "Cambié oro por plata" ("I traded gold for silver").
The lyrics play on similar-sounding words to call out his own foolishness: "Cambié una interesante por una interesada" ("I traded an interesting girl for a gold-digger"). While his original partner loved him with empty pockets, the new girl only cared about "cuánto dinero en el banco tenía" ("how much money I had in the bank") and asked for luxury gifts like "Louis Vuitton". It is a bitter, funny, and honest lesson about letting real love slip away for a fake sparkle, ending with a hard truth: you never leave the one who built you up.