Selectivo translates to "selective." It's an interesting word because it directly relates to the song's title and central theme.
In "El Selectivo," El Fantasma uses this word to explain how he has become more discerning about who he keeps in his inner circle. He sings, "Porque me hice selectivo y mis amigos son contados" (Because I became selective and my friends are few), highlighting his choice to surround himself only with those who supported him through tough times.
In "El Selectivo," El Fantasma tells a story about what happens when success arrives. He insists that money hasn't changed him at his core: "Soy el mismo que antes era" (I'm the same one I was before). However, his newfound success has made him re-evaluate his friendships. He's become "selective" about who he keeps around, cutting off people who only call to ask for favors or who talk badly about him behind his back.
So, who makes the cut? The singer reserves his time for the loyal friends who stood by him and believed in him "cuando andaba bien jodido" (when I was really broke). These are the people who don't need an invitation to his home. As for the critics who claim his success is just "pura suerte" (pure luck), he has a simple message: they can keep talking while he just gets stronger.