(also written QED and QED) is an initialism of the Latin phrase quod erat demonstrandum, meaning "what was to be demonstrated", or, less formally, "thus it has been demonstrated".
证明完毕/证讫,又写作Q.E.D.。这是拉丁片语“quod erat demonstrandum”(这就是所要证明的)的缩写,译自希腊语“ὅπερ ἔδει δεῖξαι”(hoper edei deixai),并经常被戏称为“quite easily done”(十分容易就完成了)。很多早期数学家用过,包括欧几里得和阿基米德。“Q.E.D.”可以在证明的尾段写出,以显示证明所需的结论已经完整了。
均摘自维基百科