These two currencies are referred to as native coins. This means that if a network based off of the ICON blockchain was run, either as a test network, a side-chain, or an independent network, then that new network would contain two currencies with equivalent functionalities.
As explained in the documentation sections on Governanceand Network, ICON Network contains actors calledDelegates or Validators. These actors are responsible for some important actions that determine whether the entire network is useful or not. Because of this, the delegates are rewarded for good, efficient behavior and are penalized for bad, inefficient behavior. Read more about this system in the section entitled Rewards & Penalties.