You have learned Vault

[Ciocolici]

Can somebody explain what this technique or whatever is?

Cho said it has something with jumping over mountains or with windwalking or ... I have no idea... to do..

I'll provide a screenshot: link

[LunaticAzure]

Vault is a very minor thing, it lets you jump over small-medium obstacles such as fences, rocks, etc while your windwalking. Only benefit is  you do a new jump animation that may or may not save you time compared to just regular jump. Overall it's useless, in my opinion it's somewhat satisfying to watch the animation. If you want to test/mess with it, run into a fence and press jump once you can't move forward anymore.