$STEEM is one of the base layer coins on the Steem blockchain.
It is distributed via the Proof-of-Brain (PoB) mechanism which rewards content creators and curators for their efforts on-chain. This comes out of the reward pool.
This is a cryptocurrency that is traded on exchanges. When the coin is staked, it turns into Steem Power, which is used in voting for governance issues along with on posts/comments.
$STEEM is held in the blockchain wallet which also provides feeless transactions.