1. Quod Erat Demonstrandum

Latin phrase which translates to "which was to be demonstrated". The letters QED are typically seen at the end of a mathematical proof. Some may joke that it stands for "quite easily done". Sometimes the alliterative English abbreviation WWWWW is used, meaning "which was what was wanted".

A less common variation is "Quod esset demonstrandum", which (according to florifundator) translates to "what should be proven".

QED's brother, QEF, stands for "quod erat faciendum" and translates to "which was to be done".

2. Quantum Electrodynamics

"Quantum Electrodynamics is a relativistic quantum field theory that explains the behavior of electromagnetic fields." This theory describes the quantum behavior of light so successfully that it can account for the tiniest variations in atomic spectra. Feynman was one of the originators of the theory and invented the Feynman diagram to ease calculations.

more...

3. TV Series

"Television series from 1982 starring Sam Waterston as Quentin E. Deverill, an eccentric American inventor who solves mysteries in Edwardian England. I remember it as being whimsical and charmingly odd, traits which (Northern Exposure notwithstanding) tend not to attract boffo ratings."
--Quizro

The American series ran six episodes on Tusdays between March and April of 1982.

      1- 1     23 Mar 82   Target: London
      1- 2     30 Mar 82   The Great Motor Race
      1- 3      6 Apr 82   Infernal Device
      1- 4     13 Apr 82   The 4:10 to Zurich
      1- 5     20 Apr 82   To Catch a Ghost
      1- 6     27 Apr 82   The Limehouse Connection

Source: http://epguides.com/QED/

Episodes were broadcast on CBS (America) and ITV (England) television channels. Each lasted 60 minutes and was broadcast in mono.

The series was also lesser known under the name "Mastermind".

4. Quantum Effect Devices, Inc.

Quantum Effect Devices, (Nasdaq: QEDI) is a leading provider of high-performance, cost-effective MIPS RISC embedded microprocessor solutions.

Originally a design consultancy firm, designing MIPS microprocessors for Integrated Device Technology (IDT), they now build and market their own products.

In July 2000, broadband semiconductor technology provider PMC-Sierra announced its plans to merge with Quantum Effect Devices in a stock swap valued at USD$2.3 billion.