backstage

...In most cases, it is located at the back or rear of the stage, and is separated in some way (by a curtain, wooden partition, wall, etc.). In the history of Western theater, the structure of this "dressing room" (for example, called skēnē in Greek, or dressing room or backstage in English) and its position in the theater (and in the society in which it is located) are not particularly considered, but the situation is somewhat different in traditional Japanese theater. Apart from the fact that in some folk performing arts, the dressing room is considered sacred because it is a place where people transform into something other than human, as shown by the words "inside the dressing room," "behind the dressing room," "out of the dressing room," "starting a fire from the dressing room," and other expressions that were born mainly during the heyday of Kabuki and are still commonly used today, the dressing room can be considered a special space in which the distinction between being "inside" and "outside" was strongly conscious (just like the theater it encompasses). ...

*Some terminology explanations that mention "backstage" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…多くの場合，舞台の後部あるいは背後にあって，なんらかの形(幕や板仕切りや壁など)で仕切られている。欧米の演劇史で，この〈楽屋〉(たとえばギリシア語でskēnē，英語でdressing roomとかbackstageと呼ぶ場所)の構造やその劇場(ひいてはそれが置かれた社会)の中に占める位置が，とりたてて問題にされることはあまりないが，日本の伝統演劇ではやや事情が異なる。いくつかの民俗芸能で，楽屋が人間以外のものに変身する場所ということから神聖視されることを別にしても，歌舞伎の盛んな時代を中心にして生まれ，今日もなお普通一般に用いられる語句，すなわち〈楽屋内（うち）〉〈楽屋裏〉〈楽屋落ち〉〈楽屋から火を出す〉といった言葉が示すように，楽屋はその〈うち〉にあるか〈そと〉にあるかの区別が(それを包含する劇場同様に)，強く意識された特殊な空間であったと考えることができよう。…

※「backstage」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報