Salvaje translates to "wild" or "savage." While it can describe animals or untamed nature, in this song, it's used to describe a "deseo salvaje" (wild desire).
This word is interesting because it intensifies the emotion, suggesting a powerful, untamed longing that is difficult to control. It's a strong, evocative adjective that makes the desire feel primal and overwhelming, perfectly setting the tone for the song's theme of intense yearning.