This slang is popular among young people, but teachers can't understand it.

slang 是名词，指"俚语"，即非正式、口语化的词汇或表达方式，通常只在特定群体或场合中使用。这个词来自古英语，原指"语言"或"说话方式"，后来特指非正式的语言变体。