http://www.nasa.gov/topics/aeronautics/features/trl_demystified.html
“Each TRL represents the evolution of an idea from a thought, perhaps written on a cocktail napkin or the back of an envelope, to the full deployment of a product in the marketplace.”
“The lowest level, TRL 1, indicates that information already learned from basic scientific research is taking its first step from an idea to a practical application of a lesson learned.”
“A technology that has achieved TRL 9 is one that has been incorporated fully into a larger system. It has been proven to work smoothly and is considered operational.”