Jon Udell calls it reader-created context and explains:
Everything about this buzzphrase annoys me. First, calling people “users” is pernicious. It distances and dehumanizes, and should be stricken from the IT vocabulary (see Those clueless users) as well as from the publishing vocabulary. IT has customers and clients, not users. IT-oriented publishers have readers, not users.
Second, “content” is a word that reminds me more of sausage than of storytelling (see Sausage, traffic, and clueless users). As writers and editors we don’t “generate” “content,” we tell stories that inform, educate, and entertain — or should.
Now that the original vision of a two-way web is finally made real, we can distinguish between amateur storytellers (in the best and highest sense of amateur) and professional storytellers. Thanks to the contributions of the amateurs — who are of course professional practitioners of the disciplines that we “cover” — we can tell deeper, richer, more well-informed stories about the products and services they create, and the work they do. Those stories are valuable, and the business I want to be in is based on that value, not on the “monetization” of “user-generated content”.