Quantitative tightening (QT) is a monetary policy tool used by central banks to reduce an economy's money supply, liquidity, and overall level of economic activity.
QT implementation necessitates a delicate balance between removing money from the system and not destabilising financial markets. Central banks run the risk of removing liquidity too quickly, which can frighten financial markets, resulting in erratic bond or stock market movements. This is exactly what happened in 2013 when Federal Reserve Chairman Ben Bernanke simply mentioned the possibility of slowing asset purchases in the future, causing a massive spike in treasury yields and sending bond prices lower.