Borrego literally translates to "lamb" or "sheep". While it might seem like a simple animal, in Mexican Spanish, it can also be used as slang.
In the context of this song, which tells a story of rising from poverty through illicit means, "El Borrego" is likely a nickname or a code name for a person involved in the drug trade. This double meaning makes the word intriguing and hints at a deeper, more complex narrative within the lyrics.
This song tells a story about someone who started out very poor, doing errands to get by. They wanted to advance, and one day, they "vieron drogas" [saw drugs]. It seems like this person had courage and intelligence, and the world was their rhythm.
Things were going great for a while, with "libras de todo" [pounds of everything] always being where they were supposed to be. But then, the story takes a turn. This person, who had become a "súper éxito" [super success], was also "detenido por un millón de billetes verdes" [detained for a million green bills]. It's a wild ride about someone making a lot of money and living much better, but it comes with a price. The song even mentions a moment of disbelief, "aún no comprendo cómo es posible" [I still don't understand how it's possible], when things went wrong, ending with a dramatic scene involving police and a tragic outcome for some.