Taper antrum refers to the 2013 collective reactionary panic that caused US Treasury yields to spike after investors learned that the Federal Reserve was slowly putting a brake on its quantitative easing (QE) program.
The main concern behind the taper hysteria is the fear that the market will collapse as a result of the end of quantitative easing.
In the end, the panic around the taper was unjustified as the market continued to recover after the start of the taper program.