Cash is the amount of underlying balance owned by this oToken contract. One may query the total amount of cash currently available to this market.
OErc20 / OEther
function getCash() returns (uint)
RETURN: The quantity of underlying asset owned by the contract.
OErc20 oToken = OToken(0x3FDA...);
uint cash = oToken.getCash();
const oToken = OEther.at(0x3FDB...);
const cash = (await oToken.methods.getCash().call());