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QED is a short way of writing a Latin phrase, quod erat demonstrandum, which means something like “which is what we had to show.” You put it at the end of a maths proof or a careful argument, as a little flag that says: there, that proves it. In English, people also use it a bit jokingly after a fact that seems to settle a quarrel: he said he was not hungry, then he ate three plates — QED. It is school and university language. In a proof it is normal; in everyday chat it sounds a bit pleased with itself. The same three letters can also name a hard kind of physics, but that is not this word.
證畢、證訖（數學證明結尾的拉丁縮寫。台灣課本與老師多半直接寫 Q.E.D.，不必譯成一句完整中文。）
組成From the Latin phrase quod erat demonstrandum: quod (which) + erat (was) + demonstrandum (to be shown or proved).
原始詞典資料2 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
QEDnoun詞源 1/ˌkjuːiːˈdiː/
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natural-sciencesphysical-sciencesphysics(Partial) initialism of quantum electrodynamics.
- QCD is a theory of quark interactions much analogous to QED: the interaction is carried by "gluons" (analogous to photons) which couple to the "color" (analogous to charge) of the quarks.
- By the way, these days QED is considered a relatively simple example of a quantum field theory.
這個拼法也被記錄為下列字的變化形：
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。