Double Jump
You can jump a second time by pressing Jump when Rose is in the air.
How to obtain
Defeat Death in the Choir at Notre-Dame. Then visit the Double Jump tutorial point marked on the map and complete its story scene. Winning the fight alone does not unlock the skill; the earlier Catacombs encounter does not count as this boss fight.
Backstory
The greatest acrobats in medieval Europe could appear as though they were jumping off of thin air.