Abriles literally means "Aprils," the plural of the month April. However, in this context, it's used as a colloquial way to refer to "years."
In the song, the lyric "28 abriles tras las rejas no es sencillo" (28 Aprils behind bars is not easy) refers to 28 years spent in prison. This unique usage makes the word interesting and memorable, as it's not a common way to express years in everyday Spanish.
This song is a corrido, a type of narrative Mexican folk ballad, told from the perspective of a famous real-life figure. The narrator identifies himself as Rafa Caro, a man who has spent "28 abriles" (28 years) behind bars. He looks back on his life without regret, accepting the path he has taken.
He contrasts the public's perception of him with his own identity. While the press may paint him as a "diablo" (devil), he sees himself as a realistic and respectful "ranchero" (man from the countryside). He fondly recalls his humble childhood in Badiraguato, remembering specific places and moments from his youth. The song is a reflection on a life of notoriety, imprisonment, and a deep connection to one's roots.