The term "Braceros" mostly describes "immigrants from Mexico who had contracts to work in America, mostly in agriculture" The term comes from the Spanish "Brazos" (Arms) and it makes reference to the fact that Mexicans work mainly with their when involved in agricultural work.
It is necessary to mention that not all "Braceros" have contracts to work, a lot of them just cross the border as " Mojados" -because they cross the Bravo River as illegal inmigrants and get wet, therfore the term Mojado (wet).