Bull Steepener

What Does Bull Steepener Mean?
A change in the yield curve caused by short-term rates falling faster than long-term rates, resulting in a higher spread between the two rates.

Investopedia explains Bull Steepener
A steepener differs from a flattener in that a steepener widens the yield curve while a flattener causes long-term and short-term rates to move closer together. When the yield curve is said to be a bull steepener it means that the higher spread is caused by the short-term rates, not long-term rates.