Geometer's sign-off

• "That which was to be demonstrated," in proofs
• "Proved!" letters
• Letters for a proof reader
• Logician's "and, therefore"
• Geometric sign-off
• Abbr. after a series of equations, maybe
• Logician's "as was proven"

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
QED \Q.E.D\, QED \QED\(k[=u]"[=e]*d[=e]"), interj. [From Latin, quod erat demonstrandum, i.e. which was demonstrated.] Which was demonstrated; -- a phrase used after the conclusion of some line of reasoning, especially in mathematical or logical proofs. ...

Wikipedia Word definitions in Wikipedia
QED is a line-oriented computer text editor that was developed by Butler Lampson and L. Peter Deutsch for the Berkeley Timesharing System running on the SDS 940 . It was implemented by L. Peter Deutsch and Dana Angluin between 1965 and 1966. QED (for "quick ...