Sterilization

What Does Sterilization Mean?
A form of monetary action in which a central bank or federal reserve attempts to insulate itself from the foreign exchange market to counteract the effects of a changing monetary base. The sterilization process is used to manipulate the value of one domestic currency relative to another, and is initiated in the forex market.

Investopedia explains Sterilization
For example, to weaken the U.S. dollar against another currency, the Fed would sell more U.S. dollars and buy the foreign currency. The increased supply of the U.S. dollar would lower the value of the currency. The Fed would do the opposite if it wanted to strengthen the U.S. dollar.