Noun

1. A Mexican-American, especially a juvenile delinquent in the Los Angeles area.

   1998. They asked him if he was a pachuco. He said all the pachucos he knew of lived in El Paso. He told em he didn’t know any Mexican pachucos. — Cormac McCarthy, Cities of the Plain

Adjective

1. (Mexican) flashy, flashily dressed
2. (Costa Rican) slang (often considered low-class)