Market maker of last resort
From ACT Wiki
Financial markets - central oversight.
Market maker of last resort describes exceptional market intervention by a central bank.
In normal times, central banks support market liquidity by providing liquidity insurance to individual institutions.
Exceptionally, a central bank may stand ready to act as a temporary market maker of last resort, to improve the liquidity of one or more markets whose illiquidity posed a threat to financial stability, or was judged to be important to the transmission mechanism of monetary policy.