Trampolín literally means 'trampoline', the bouncy device used for jumping. It is an unusual and memorable word to find in song lyrics, since it is normally reserved for playgrounds and gymnastics.
In this song, the word is used metaphorically. The narrator sings "Mi persona le sirvió de trampolín en mi" (my person served as a springboard in my), meaning the other person stepped on their generosity to get ahead.
This song, "El Trampolín," is a really blunt and honest look at betrayal and ungratefulness. The singer talks about how he helped people, saying, "mi persona le sirvió de trampolín" [my person served as a trampoline for them]. He feels like his generosity was taken advantage of, and that these people "aprovecharon a su modo" [took advantage in their own way]. He even says, "un pedazo del pastel yo me comí, traigan hambre y se lo tragaron sólo" [I ate a piece of the cake, they brought hunger and just swallowed it whole], highlighting how little was left for him.
It's all about those who forget where they came from once they find success. The singer warns that "la vida y la miseria le refresca la memoria" [life and misery refresh their memory] when things turn around. He admits, "me di cuenta que no fue buena idea sea un lobo a pastorear mis ovejas" [I realized it wasn't a good idea for a wolf to shepherd my sheep], showing his regret for trusting the wrong people. He's learned a hard lesson, and now he's moving on, telling them, "nos vemos a la vuelta" [see you on the flip side].