The RSK (Rootstock) blockchain is a smart contract blockchain operating as a Bitcoin sidechain and supporting several DeFi platforms.
RSK uses Smart Bitcoin (RBTC) as its utility token. RBTC is used to pay smart contract fees on the RSK blockchain just as ETH is used to pay fees on the Ethereum blockchain.
Smart Bitcoin (RBTC) is pegged 1:1 to the price of Bitcoin (BTC). As the RSK blockchain is a sidechain of Bitcoin, there is a two-way peg between RBTC and BTC, and the two assets can be sent back and forth interchangeably between the two blockchain networks.