The relative change in the yield for each treasury maturity is known as a shift in the yield curve. When the change in the yield for all the maturities is same, then there is a parallel shift in the yield curve; and when there is change in yield for all the maturities is not same, then there is a non-parallel shift in the yield curve.

There are two types of non-parallel yield curve shifts:

1. A twist in the slope of the yield curve refers to the flattening and steepening of the yield curve. When the slope of yield curve decreases then it is known as flattening of the yield curve. When the slope of yield curve increases then it is known as the steepening of the yield curve.

2. The second type of non-parallel yield curve shift is a change in the humpedness or curvature of the yield curve. These shifts involve the relative movement of yields at the long and short maturity sectors of the yield curve relative to the intermediate maturity sector of the yield curve. Such kind of non-parallel shift which changes the curvature of the yield curve is known as butterfly shift. Here, the intermediate maturity sector can be viewed as the body of the butterfly, and the short and long Maturity Sectors can be viewed as the wings of the butterfly.

Figure 1: Parallel Shifts of the Yield Curve

Figure 2: Non-Parallel Shifts of the Yield Curve

(a) Flattening

(b) Steepening

(c) Butterfly Shift (i) Positive

(d) Butterfly Shift (i) Negative