1. 「女子高生/女子校生 (Joshi Kōsei)」 High school girl.
2. 「常識的に考えて (Jōsikiteki ni Kangaete)」 Think with common sense.
3. 「情熱的に考えて (Jōnetuteki ni Kangaete)」 Think passionately.
4. 「じつは巨乳 (Jitsuha Kyonyū)」 Actually big breasts.
5. 「じつはキツネ (Jitsuha Kitsune)」 Actually a fox.
6. 「冗談でしょ! (Jōdandesho!)」 Just Kidding!
7. 「冗談、顔だけにしろよ! (Jōdan, Kaodakenisiroyo!)」 Just kidding, keep it to yourself!
8. 「次長課長 (Jityō Katyō)」Deputy section chief.
9. 「自衛官 (Jiei Kan)」 A JSDF officer, more commonly written 「J官 (J-kan)」.
10. 「JR京浜東北線 (JR Keihin-Tōhoku Line)」 Station numbering on the JR Keihin-Tōhoku Line or Negishi Line.
11. 「喜多村純子 (Junko Kitamura)」 A character from the series 「ひみつ探偵JK」.
12. 「神宮海蔵 (Jingū Kaizō)」
13. 「ジャスティスナイト (Justice Knight)」 See the article 「ハナJK (Hana JK)」.
14. 「ハナJK」 The model name of the third Jeep Wrangler.
It is said that the meaning of "high school girl/female school student" was originally a slang term used by illegal underground websites dealing in compensated dating to avoid police crackdown. (Child prostitution targets people under 18, but before the lowering of the age of adulthood, 18- and 19-year-olds were also targets of the crime, so it was necessary to use a slang term.)
However, it gradually came to be used in legal environments as it was mixed with internet slang such as "KY," and it also began to be used by major media outlets in content aimed at young people, so its meaning as a slang term was lost.
Currently, derivative forms such as "DK" for danshi kōkōsei (high school boy) and "JC" for joshi chūgakusei (junior high school girl) are also used.