It is a nickname for a scheme run in Northern Ireland which subsidised renewable fuel over fossil fuels. Technically known as RHI, the Renewable Heat Incentive, it is in the spotlight because it turned out to be far more costly to the taxpayer than planned. Sinn Fein's Martin McGuinness resigned as second minister over it, saying the DUP's Arlene Foster, the first minister, had a conflict of interest over the scheme.
Following the firing of FBI Director James Comey by President Donald Trump, Democrats and others have been calling for a "special prosector" to be assigned. What is a special prosecutor and what do they do?