which was to be shown or demonstrated (used especially in mathematical proofs).
Origin of Q.E.D.
First recorded in 1810–20, Q.E.D. is from the Latin word quod erat dēmōnstrandum
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
1760, abbreviation of Latin quod erat demonstrandum "which was to be demonstrated."
Online Etymology Dictionary, © 2010 Douglas Harper