Plebada is a colloquial term, particularly common in Mexico, that refers to a group of friends, a crew, or a gang. It's a more informal and regional word than common alternatives like amigos or grupo.
In the context of
Get ready to cruise with Luis R Conriquez and El Rabbanito in "Todo Bien"! This song is all about living the good life, Mexican corrido style. Luis R tells us right away that he's been spotted "muy cerquita de Durango" [very close to Durango], and he's growing some seriously "apestosa" [stinky] weed. And why not? It's selling everywhere, even in Los Angeles!
He's gone from a skateboard to an AMG, rocking "Ropa Amiri, LV" [Amiri, LV clothes] while cruising the LA freeways. Everything's good, "Todo bien." He's also moving product across the border, making money, and hanging out "en Culiacán con la plebada" [in Culiacán with the crew], where he's "al cien" [at 100% or doing great]. He's testing out his Porsche Coupe and AMG, and the "Merca pa' vender" [merchandise to sell] comes from LA. It's a fun, boastful look at success and the fast life.