You've learned Charge Jump! To use this ability, hold W (LT/L2) then press Space (A/X) to leap extra high into the air!
Charge Jump is the final skill Ori learns to progress (excluding optional skills from the definitive edition) Holding down W (LT/L2 on consoles) while on the floor will charge up the jump. While the jump is fully charged, press Space/Z (A/X on consoles) to boost up into the air. Holding down the button will also make you jump higher.
You can also charge jump while holding onto a wall. You do this by pressing and holding either Left or Right (Left Analog Stick) in the direction pointing away from the wall. Ori will start holding out their hand and a line will appear indicating the direction to jump. While it is charged, you can then move the line with Up and Down (Left Analog Stick). To jump off the wall in the direction of the line, press Space/Z (A/X on consoles) like on the floor.
It also deals a lot of damage, so it's useful for attacking enemies up in the air, such as the ones in Mount Horu, Charge Jump can kill them in one hit.