Alelí refers to a type of fragrant flower, specifically a wallflower or gillyflower. It's a beautiful and somewhat uncommon word in everyday Spanish, making it stand out in the lyrics.
In the song, the phrase "lila alelí" evokes a vivid image of a purple flower, symbolizing beauty, tenderness, and perhaps a delicate, hidden love. The artist uses it to paint a poetic picture of a dream or a cherished feeling, making it a memorable and enchanting word choice.
Silvana Estrada spends this whole song not saying the thing. She stays "Callada junto a tu almohada" (Silent beside your pillow), and the feeling still gets out sideways as "Un calor que me estremece" (A warmth that makes me shiver). The person she is singing to has no idea, which is the point. She even names what never happened: "La flor que nunca te di" (The flower that I never gave you). An alelí is a wallflower, and a lilac one is the gift she kept in her pocket.
Then she gives up, sweetly. The chorus is "Ay, ay, ay, ay, llévatelo todo" (Oh, oh, oh, oh, take it all), and the reason lands one line later: "Que sin ti, aquí, nada crece" (That without you, here, nothing grows). She packs up for the countryside and leaves her smile behind, because "¿Sin ti para qué la quiero?" (Without you, why do I want it?). Her love gets parked where nobody has to deal with it: "Mi amor es como un lucero" (My love is like a star), one that shines behind the blue of the sky whether or not anyone looks. The long wordless laralala stretch at the end says more than another verse would have.