A term used to describe various 'enhanced' foods (nutriceuticals). Though consensus on an exact definition is lacking, I am rather fond of 'foods that may provide health benefits beyond basic1 nutrition'.
Stephen DeFelice, founder and chairman for the Foundation for Innovation in Medicine, provided a very broad definition when he coined the expression:
"any substance that may be considered a food or part of a food, and provides medical or health benefits, including the prevention and treatment of disease."
Uses extend beyond the medical and therapeutic (for example, providing blood clotting agents in milk - see pharming) to include aspects related to general health and disease prevention (such as antioxidants) and improved nutrition (eg. increasing calcium levels)...and the recreational (LSd iN y0Ur COrNfl4kEs, anyone? Pussy ;p Gingki biloba then?).
Could be construed as a fancy (and expensive) way of listening to Grandma: eat your broccoli; bona-fide chicken soup for colds; cranberry for urinary tract infections...
Note that a distinction between 'normal' foods that have been supplemented and gengineered/selectively-bred varieties of crops 'n' cattle with higher than normal levels of, say, vitamins is not here made.
1 So as not to discount foods such as the much-vaunted 'yellow rice'.