Wetback is a very offensive insult in American English for a Mexican person — originally for someone who entered the United States without permission by crossing the Rio Grande, the river on the border, and so arrived with wet clothes. Please do not use this word. It sits with the strongest racial slurs in American English: saying it, even as a joke, will shock people and can end a conversation, a friendship, or a job. You need to know it only so that you understand what is happening when you meet it in a film, a novel, a history book, or an old newspaper. It also carries real historical weight — in 1954 the US government ran a mass deportation programme and actually named it "Operation Wetback", which is why the word appears in serious history writing about the border. In such writing it is usually put in quotation marks or discussed as a slur, not used plainly. If you need to talk about the topic yourself, the neutral words are "undocumented immigrant", "migrant", or "migrant worker".

極度冒犯的種族歧視字眼，指（非法越過美墨邊界的）墨西哥人。請勿使用；只需能看懂。中性說法是 undocumented immigrant（無證移民／移工）。