■ The words ＯＢ and ＯＧ are used to refer to graduates or former students of schools and universities, former members of clubs, etc. The terms are often equivalent to 先輩（せんぱい）, which means a person who is senior to one within an organization, especially among the students or graduates of a school.
□ ＯＢ is an abbreviation for "old boy" and ＯＧ for "old girl." "Old boy" and "old girl" are used in Britain and elsewhere to refer to the people who have graduated from a particular school or university; this is presumably the source of the Japanese abbreviations. The word ＯＢ is found in Japanese novels and dictionaries from the 1930s and perhaps earlier; ＯＧ may have come into use later.
Two related terms are ＯＢ会（かい） and ＯＧ会, which are informal terms for alumni associations or clubs.
◇ 最近､早稲田大学就職課と称し､学生・OBの自宅に電話をかけ、就職活動の状況や内定企業名、勤務先等々の個人情報を聴取するという、被害が多発しています。軽率に対応することなく、充分に注意してください。(Web, July 2000)
(Here, OB refers to alumni, presumably both male and female, of Waseda University.)
あるＯＢの方との面談の際に，「君は志望動機なんかはしっかりしているのに，自己ＰＲは弱いな」といわれたことがありました。(Web, July 2000)
(In this example, the ＯＢ is providing career advice to a student at his alma mater, so ＯＢ seems equivalent to 先輩.)
はじめまして。私は横浜市立大学人形劇団どんぶらこのＯＧです。卒業して３年目になってしまった今年、夏に公演を企画中です。(Web, July 2000)
(Here, ＯＧ refers to a woman who used to be a member of a university puppet troupe.)
本学には「就職が良い」という理由で入学して来る学生がかなりいます。先輩ＯＧが種々の企業で熱心に働き、高い評価を得ていて求人につながるという好循環にあります。(Web, July 2000)
神戸学院大学軟式テニスサークルＯＢ会(Web, July 2000)
秋桜会って？・・・星好きの会でーす。もともとは、横浜にある某有名（かもしれない）女子高天文部のＯＧ会。会員数１０名前後で、細々と活動してます。(Web, July 2000)
This entry was created by Tom Gally, with additional contributions by Brian Chandler and Jim Breen.
Created 2000-07-09. English usage of "old boy" and "old girl" elucidated by BC and JB 2000-07-10.