Nerd通常被翻译成怪胎、怪咖，是英语俚语中一个稍含贬义的用语，一般指偏爱钻研书本知识，将大量闲暇用于脑力工作，对流行文化不感兴趣，而不愿或不善于体育活动或其他社会活动的人。在美国中学和大学文化中则通指那些专心一致刻苦学习的学生。在华人圈内相同的概念是“书呆子”或“书虫”，古称两脚书橱。而近年来，Nerd已经逐渐从贬义词变成了具有自豪感和身份认同意义的词语。不过在美国偏乡地区校园内，这样的人依然显著地被排挤。

Nerd在美式英语中相对的词语是Jock，指擅长体育、四肢发达、头脑简单、异常自信且热爱泡妞的人。

Nerd (adjective: nerdy) is a descriptive term, often used pejoratively, indicating that a person is overly intellectual, obsessive, or lacking social skills. They may spend inordinate amounts of time on unpopular, obscure, or non-mainstream activities, which are generally either highly technical or relating to topics of fiction or fantasy, to the exclusion of more mainstream activities. Additionally, many nerds are described as being shy, quirky, and unattractive, and may have difficulty participating in, or even following, sports. Though originally derogatory, "Nerd" is a stereotypical term, but as with other pejoratives, it has been reclaimed and redefined by some as a term of pride and group identity.