Muñecas de porcelana literally translates to "porcelain dolls," fragile, beautiful figures that are easily broken. As the song's title, the phrase carries deep symbolic weight about delicate hearts.
The lyric "Un amor de muñecas de porcelana" ("A porcelain doll love") uses the image to describe two people who, despite their fragility and past wounds, find gentle comfort and love in each other.
Don Omar spends this one telling a story instead of building a hook. Marta is 23, has her own apartment, and won't date anyone since a man named Carlos left her "El mismo día de su boda" [on the very day of her wedding]. Nilda is the same age, tougher, and carries her own wound: her father touched her as a kid. The two of them end up together, and the song treats that as a plain fact of the story rather than a twist to build toward.
The hook calls them "Un amor de muñecas de porcelana" [a porcelain-doll love], fragile and easily judged, which is how everyone around them sees two women in love. Don Omar doesn't argue the point so much as flatly refuse to entertain the opposite one: "No hay quien halle pecado en esta relación" [no one can find sin in this relationship], "Pues el sufrimiento ya las redimió" [because the suffering already redeemed them]. The song closes with "Dos amigas" [two friends] "Que juegan a las muñecas" [who play with dolls], turning the title from a metaphor about fragility into a literal memory of when they were girls.