High Quality Content by WIKIPEDIA articles! Q.E.D. is an initialism of the Latin phrase quod erat demonstrandum, which translates as "which was to be demonstrated". The phrase is traditionally placed in its abbreviated form at the end of a mathematical proof or philosophical argument when what was specified in the enunciation — and in the setting-out — has been exactly restated as the conclusion of the demonstration. The abbreviation thus signals the completion of the proof.