A consumer who is an amateur in a particular field, but who is knowledgeable enough to require equipment that has some professional features. [professional + consumer]
In the parlance of the tech world, the new generation of digital film equipment is designed for the ‘prosumer,’ the consumer who thinks of himself as a semi-professional
—Doug Bedell, “Digital video revolution,” The Dallas Morning News, October 12, 2000
This is far from the cheapest DV model; you can find others for as little as $600. This is far from the most versatile model; “prosumer” units like Canon’s $3,500 XL1 offer professional features like interchangeable lenses, a user-controllable shutter and more flexible audio.
—Stephen Manes, “Little Big Cam,” Forbes, October 16, 2000
Next spring, Sony will introduce an upgraded version... The product will be directed to the ‘prosumer’ videophile segments.
—HFD, November 23, 1987 (OED)
Besides the definition I've provided, this word can also refer to 1) A person who helps to design or customize the products they purchase (producer + consumer); 2) A person who creates goods for their own use and also possibly to sell (producing + consumer); and 3) A person who takes steps to correct difficulties with consumer companies or markets and to anticipate future problems (proactive + consumer).
Thanks to LeAnne Baird and Gerry Pareja for prodding me to post this word. I was reluctant because this is not only an old word, but also a very slippery one. The second sense of the term — the producer consumer — was invented by Alvin Toffler back in 1979 in his book The Third Wave. The “professional consumer” sense of the word first emerged around 1987, and is now the most common sense.
Checking the citations for all senses on the complete Lexis-Nexis database of newspaper and magazine articles, an interesting pattern emerges:
As you can see, the use of this word has increased quite steadily, particularly since 1995, which would be around the time when it became associated with the video equipment market. (Prosumer is a well-accepted category for camcorders, VCRs, and other video playthings.)