Definition:

The process of using specific brand names of products as names for the products in general. 

In numerous cases over the past century, the colloquial use of a brand name as a generic term has led to the loss of a company's right to the exclusive use of that brand name. (The legal term for this is genericide.) For example, the common nounsaspirin, yo-yo, and trampoline were once legally protected trademarks.

(In many countries--but not in the United States or the United Kingdom--Aspirin remains a registered trademark of Bayer AG.)

See Examples and Observations below. Also see:

• Genericide
• Introduction to Etymology
• Trademark
• Where Do New Words Come From?
  

Etymology:
From the Latin, "kind"

Examples and Observations:

• "The words kleenex and xerox illustrate [a] technique for creating new words . . .. Kleenex, a brand name for facial tissue, has come to denote facial tissue in general. Xerox is the name of the corporation that produces a well-known photocopying machine, and much to the dismay of the company, the term xerox has lost its specific brand-name connotation and has come to be used to describe the process of photocopying in general."
  (A. Akmajian et al. Linguistics: An Introduction to Language and Communication. MIT Press, 2001)
• Generification and Dictionaries
  "A surprising number of words have developed contentious generic meanings: they include aspirin, band-aid, escalator, filofax, frisbee, thermos, tippex, and xerox. And the problem facing the lexicographer [dictionary-maker] is how to handle them. If it is everyday usage to say such things as I have a new hoover: it's an Electrolux, then the dictionary, which records everyday usage, should include the generic sense. The principle has been tested several times in the courts and the right of the dictionary-makers to include such usages is repeatedly upheld. But the decision still has to be made: when does a proprietary name develop a sufficient general usage to be safely called generic?"
  (David Crystal, Words, Words, Words. Oxford University Press, 2006)

• From Brand Names to Generic Terms
  "Some brand names have slipped the leash, run wild, and joined the pack of the general vocabulary. Here are some of them:
   
  • elevator and escalator: Both originally trademarks of the Otis Elevator Company.
  • zipper: A name given to a 'separable fastener' by the B.F. Goodrich Company many years after it was invented. The new name helped the zipper attain popularity in the 1930s.
  • loafer: For a moccasin-like shoe.
  • cellophane: For a transparent wrap made of cellulose.
  • granola: A trademark registered in 1886 by W.K. Kellogg, now used for a 'natural' kind of breakfast cereal. 
  • ping pong: For table tennis, a trademark registered by Parker Brothers in 1901.
  (Allan Metcalf, Predicting New Words: The Secrets of Their Success. Houghton Mifflin, 2002)
• Generification in Nigerian English
  "Pampers is, without a doubt, one of the world's biggest manufacturers of diapers, but Nigerian children--and parents--don't seem to realize that the generic name for the folded, absorbent cloth drawn up between the legs of babies and fastened at their waists to prevent excrement from spilling over their bodies is called a diaper (or a nappy in British English). Pampers is a trademark."
  (Farooq A. Kperogi, "Nigeria: The English Nigerian Children Speak." Daily Trust, September 9, 2012)