also: ジェイ
noun
J; j
The letter J itself, used in contexts like alphabet listing, abbreviations, or as a symbol.
アルファベットのＪは、ジェーと読む。
The letter J in the alphabet is read as 'jei'.
prefix
Abbreviation prefix for Japan, as in Jリーグ (J.League) or J-POP.
See also: ジャパン
Ｊリーグは日本のプロサッカーリーグだ。
The J.League is Japan's professional soccer league.
counter
joule
Counter for joules, the unit of energy.
See also: ジュール
この仕事には100Ｊのエネルギーが必要だ。
This work requires 100 joules of energy.
noun
In card games, the jack (playing card).
See also: ジャック
彼はハートのＪを出した。
He played the jack of hearts.
counter
tatami mat counter
Used on floor plans to count tatami mats as a measure of room size (approx. 1.82 sqm or 1.54 sqm).
See also: 畳
この部屋は６Ｊの広さです。
This room is 6 tatami mats in size.
ジュール is the full katakana word for 'joule', while Ｊ is the unit symbol used as a counter.
Ｊリーグ is the full name of the league; Ｊ is the colloquial shortening.
From the Latin letter J, used in various abbreviations and symbols. The reading ジェー/ジェイ reflects the English pronunciation of the letter.