In Japanese, 〆 means shime 締め, "fastening," "tightening," the noun form of the ichidan verb shimeru 締める, "to fasten," "to tighten." To elaborate: this weird-looking symbol is just a quick way to hand-write shime.
In Japanese, parentheses （）, are used in multiple ways: they can show the age, gender or other personal information after someone's name; they represent furigana 振り仮名 (ruby text) in single-line layouts; on the internet, they contain emotes, such as "lol," etc.; they similarly enclose actions in theatrical scripts; they may contain thoughts or other comments; and they surround optional phrases or alternative phrases in grammatical examples.
In Japanese, "brackets," kakko 括弧, refers to symbols that enclose text such as 【】, （）, 『』, 「」, 〈〉, 《》. They're generally like English brackets, except that Japanese brackets may get rotated 90 degrees when Japanese is written vertically.
For [], {} used in examples in this site, see Reading The Examples.
In this site, example sentences and excerpts typically follow a format of romaji, Japanese, and English translations, with symbols added to the romaji and translation in order to keep the Japanese text unchanged.
For reference, this article will list what the symbols found in the examples in this site mean.
In this site, φ, the Greek letter "phi," is used as a symbol to represent nulls (zeroes) in examples.
See Reading The Examples for other symbols used in this site.
In grammatical analysis, "null" is how you refer to something that's not uttered (pronounced or written) but is meaningful nevertheless. They're represented by either φ or ∅ (empty set). For example:
Above, φ represents a null particle (or zero particle) and a null copula (or zero copula). Compare with:
Above we have a wa は particle and da だ copula.
Although the meaning is basically the same, there are nuances between pronouncing wa/da and not pronouncing them. Also, it may look confusing how the copulas "am," "is," "are" show up in the English translation without an equivalent in Japanese, so nulls are useful in this regard.
In Japanese, a triangle (△), sankaku 三角, is sometimes used to mean an answer is partially correct. A right answer is a circle (○), while a wrong answer is either an X mark or, in school tests, a check mark (✓) or tick.
In Japanese, a circle (○), maru 丸, has multiple uses: it typically means something is "correct," that an answer is "right." In this case, "wrong" is either an X mark or a check mark (✓), and a triangle (△) is half-right. It's also used as a placeholder, specially to censor words.
This article is about the circle symbol, not about a "circle," saakuru サークル, in the sense of a group of people that do an activity like drawing doujinshi 同人誌.
In Japanese, an "X mark" (☓), batsu-jirushi バツ印, typically means an answer is "incorrect," fuseikai 不正解, although it can also mean something is dame 駄目, "not good," NG, "not allowed," "didn't work out." The opposite symbol is a "circle" (○), maru 丸. These symbols are also used as placeholders.
In anime, Gainax pose, or Gainax stance, in Japanese: gaina-dachi ガイナ立ち, literally "Gaina-standing," refers to a way for a character, usually a giant robot, or giant robot pilot, to stand imposingly as it waits for battle: with arms crossed and legs apart, due to its prominent use by animation studio Gainax, ガイナックス.(dic.pixiv.net, tvtropes.org)
In anime, when a character stands with legs apart readying their sword (or other weapon) thrusting it forward, and the camera perspective is warped so the sword looks far bigger than normal, that's called a Sunrise Stance (サンライズ立ち), Sunrise Perspective (サンライズパース), Brave Perspective, Yuusha Perspective (勇者パース), Brave Stance, Yuusha Stance (勇者立ち), Fukuda Perspective (福田パース), or, in Chinese, 大張一刀流 (Oobari Ittouryuu?).(dic.pixiv.net:勇者パース, dic.nicovideo.jp:サンライズ立ち, tvtropes.org:SwordPointing)
In Japanese, uwa'... watashi no nenshuu, hiku-sugi...? うわっ･･･私の年収、低すぎ･･･？, meaning something like "yikes... my salary, it's too low...?" is a text used in an internet ad by a job-search company called @type, which featured a woman covering her mouth in shock, presumably after realizing how little she made. The ad copy became a meme, with parodies found even in manga and anime.
In anime, placing your elbows on a desk and interlacing your fingers in front of your face such that it hides your mouth and you look like you're scheming something important is called a Gendo pose, in Japanese: Gendou Poozu ゲンドウポーズ, in reference to Ikari Gendō 碇ゲンドウ, from Neon Genesis Evangelion, Shinseiki Evangerion 新世紀エヴァンゲリオン, a bespectacled, gloved character who did this pose a lot.(dic.pixiv.net)
In Japan, a backhand slap on someone's chest, or, sometimes, doing the gesture on air, suggests the person is doing a tsukkomi ツッコミ, a "retort" calling out something stupid that someone else said, which is typically done in manzai 漫才, a type of comedy routine with a duo of comedians, namely the boke ボケ saying stupid things, and the tsukkomi calling out the boke.
In Japanese, nandeyanen なんでやねん, meaning literally "why is [it]," is a phrase popularly associated with tsukkomi ツッコミ, the act of "retorting" and the comedian doing retorts in manzai 漫才, a type of comedy done by a duo where one says something stupid (the boke ボケ), while the other "retorts" by saying they're wrong or questioning them, sometimes physically hitting them, e.g. with a backhand slap on their chest.
This phrase is in Kansai 関西 dialect, and Kansai is associated with manzai, so one can guess its popularity is due to manzai comedians from Kansai using it.
In Japanese, boke ボケ means "idiot," or something stupid someone does, specially in comedy.
