POC

Origin of the phrase

The Oxford English Dictionary has an example of the use of the phrase as early as January 22, 1967 by the Los Angeles Times.
One of the early uses of the term "proof of concept" was by Bruce Carsten in the context of a "proof of concept prototype". His usage was defined in the November 1989 Power Conversion and Intelligent Motion magazine, in a column "Carsten's Corner", (p. 38) subtitled "Let's Define a Few Terms":

Proof-of-Concept Prototype is a term that (I believe) I coined in 1984. It was used to designate a circuit constructed along lines similar to an engineering prototype, but one in which the intent was only to demonstrate the feasibility of a new circuit and/or a fabrication technique, and was not intended to be an early version of a production design.

Also defined and distinguished in the column were the terms 'breadboard', 'prototype', 'engineering prototype', and 'brassboard'.

 In a universe far far away, before any of us were alive, our guy who bought things was asked to come on loan (as it were) to a nearby kingdom up on the hill to help them buy something very big and expensive and important (to them) and so, with the blessing of his king, he set off on his donkey to the kingdom on the hill. The high wizard he was supposed to meet had sent him a letter explaining all and it told him he was to be engaged in a POC buying thing. Our guy who bought things felt that perhaps he was backward and not up to the challenge because he didn't know what a POC was, so on his way (donkeys are rather slow) he Goggled POC and discovered it was just an industry catch phrase and he knew he was ready.

The grand wizard had rented a wonderful old theater for the POC (mostly because it was cheap, because it had earthquake damage and so they couldn't show movies there anyway) and it would duly impress all the folks that would appear for the POC. (Even in universes far far away, they had movies- see Lucas) So they had the wonderful old screen set up so it would show one half of the movie in the old way and one half in the new way. So they could demonstrate Proof of Concept when they had Proof of Concept, but they didn't have it yet. Our guy who bought things invited all sorts of wizards and captains of industry and brilliant optical guys and computer geniuses, and not so surprisingly, they all wanted to come. It turned that all of them had big dollar signs in their eyes. 

It seems that once the guy who bought things, bought the Proof of Concept, then the king in this kingdom and the king in the guy who bought things' kingdom and all the other kingdoms all over the universe would want to buy a Proof of Concept as well. 
So our guy set up a long table at the front of the theater with microphones and lots of chairs and he played master of ceremonies to a group out in the theater seats of maybe a hundred people all with dollars signs in their eyes. All the wizards and experts of the kingdom sat with our guy, so he didn't have to be an expert at all. It reminded our guy of a Senate hearing. Lots of questions and answers and everyone knew everyone except for a few people no one liked so they all pretended they didn't know them.
And then all the people with dollars signs in their eyes submitted what it would cost for each of them to sell a Proof of Concept and all of them were 2 million and up. So there was a second Senate hearing where the guy who bought things told all the people with dollar signs in their eyes that the king didn't have that kind of money and they could all try again, but it had to be under $1 million. 
So one man from Taiwan resubmitted his proposal to build the Proof of Concept. All the other people shuffled out and grumbled a lot and were never seen again. Our guy who buys things, thought he saw a group of them pushing shopping carts in another kingdom far away by the ocean, grumbling and shuffling their feet and they sung "Off to work we go..." 
So the nice man from Taiwan, who knew all along how to build a Proof of Concept for cheap (He had already made untold riches by selling lots and lots of Proof of Concepts to India, where they had been Proofs of Concepts for years. He had a very nice picture of a tent theater in some remote part of India where the kids were lined up to see his wonderful Proof of Concept.

So our guy who bought things came home on his donkey and discovered a little while later that all of them were famous (except for him) for their wonderful Proof of Concept and all the kingdoms around the universe agreed to only buy the Proof of Concept from the nice man from Taiwan. And everyone lived happily ever after. And someday when someone makes a really fancy movie made out of 0s and 1s, the whole universe can watch it on their 0s and 1s movie screen.