Your definition works! I like to focus on the creative spirit of it all, whenever I define it, because that's the part that interests me most. I say it something like this:
Steemit is a stage, a spotlight, and an amplifier for the Creative Age, when we survive and thrive by our creativity. For every kind of artist, this is a playground where we find our voice, stand for what we believe in, and connect with others like us. For example, Steemit promotes creative thinking through contests and events such as the Steemit #openmic, #colorchallenge, and #culinarychallenge. Participants earn monetary rewards, along with growth opportunities in body, mind, heart, soul, and spirit, through four levels of creative thinking: observation, communication, creation, and curation.
I like that!