limón y sal literally means "lemon and salt", a combination famously paired with tequila! It's a fun and unique phrase that captures the entire message of this song.
Julieta Venegas uses this expression as a metaphor for unconditional love. She's saying she loves her partner with everything, both the sour parts (limón) and the savory parts (sal), accepting all their quirks and flaws.
Mexican singer Julieta Venegas wrote one of the most honest love songs out there with "Limón Y Sal". Instead of pretending romance is perfect, she opens with total bluntness: "Tengo que confesar que a veces no me gusta tu forma de ser" ("I have to confess that sometimes I don't like your way of being"). Her partner vanishes without explanation, ruins sunset moods by saying nothing romantic, and gets moody every full moon. Still, she accepts every single flaw because the joy of having them around outweighs the annoyances. When she sings "Sólo tenerte cerca, siento que vuelvo a empezar" ("Just having you near, I feel like I start over"), she means their simple presence resets her world.
The heart of the song lies in the title phrase: "Yo te quiero con limón y sal" ("I love you with lemon and salt"). In Mexico, pairing lime and salt is the classic way to take a shot of tequila or dress up food and beer. It makes the sour and the sharp taste good together. She uses this image to say she loves her partner complete with their bitter edges and unpredictability. Even when they are hot and cold ("si vienes o si vas" / "whether you come or go") or confused about their feelings, she asks for zero changes. It is a warm, upbeat track about loving someone fully as they are, sour bits included.