A non-parallel yield curve shift in which long- and short-term yields decrease by a greater degree than intermediate rates. This yield curve shift effectively humps the curve, adding to the curvature of the yield curve. 

|||For example, a negative butterfly shift can happen when short- and long term-rates decrease by 75 basis points (0.75%), while intermediate rates only decrease by 50 basis points (0.50%). This is the reverse of a positive butterfly, in which short- and long-term rates increase more than intermediate rates.