The most common academic definition of creativity come from Teresa Amabile:

"the production of ideas or outcomes that are both novel and useful (appropriate to some goal)"

Other definitions I've come across:

"What is creativity? The best general answer I can give is that creativity is the ability to see (or to be aware) and to respond."

-- Erich Fromm (from his essay The Creative Attitude, in Creativity and its Cultivation, 1959)

“If you asked me five years ago what creativity meant to me, I would say, “oh that’s cute. That’s fun. I don’t really DO a lot of A – R – T cuz I have a J – O – B. So you go do take your paintbrush or scrapbook and have but I’ve got shit to do. If you asked me now, it is the way I share my soul with the world. Without it, I am not o.k. Without having access to everyone else's we are not o.k. I have come to the conclusion that it is the only thing, the only unique contribution that we will make in this world will be born of creativity.”

-- Brene Brown in conversation with Liz Gilbert)

"When I refer to “creative living,” I am speaking more broadly. I’m talking about living a life that is driven more strongly by curiosity than by fear.” 
― Elizabeth Gilbert, Big Magic: Creative Living Beyond Fear

"The strange partnership between a human being's labor and the mystery of inspiration."-- author Elizabeth Gilbert in an interview

You can find even more definitions here.