The best general definition of innovation I know (and I’ve done a lot of research on the topic) is from The Diffusion of Innovations by Everett Rogers, first published in 1962:
“An innovation is an idea, practice or object that is perceived as new by an individual or other unit of adoption.”
I like this because it’s value-neutral–innovations can be beneficial for certain groups but detrimental to others (for example, the widespread use of automobiles certainly hurt the manufacturers of horse-drawn carriages). Also, Rogers stresses that what matters is the PERCEPTION that the innovation is new–something that is old news to one person may be new and “innovative” to another. The degree to which something is “innovative” is related inextricably to its context.