I'm fairly new to Steemit as well. I've looked up an exact definition of Steemit, hopefully that will help!

It says that Steemit is a social news community. "Steemit is a blogging and social networking website that uses its Steem blockchain-based rewards platform for publishers. The Steem blockchain produces Steem and Steem Dollars which are tradable tokens obtained for posting, discovering, and commenting on content."
The quote is from Wikipedia.org.

I hope this helps answer your question! :)