Ramp Jump
While sharing a part of their name with the later introduced ramp slides, ramp jumps are the exact opposite. While ramp slides make you gain speed and lose height ramp jumps make you lose speed and gain height by slamming your body into an upwards slanted non-walkable surface.
Execution
While the principle behind ramp jumps might sound easy, performing one is far from it. You need a decently slanted surface to boot. After you found a fitting one your next step is to build speed and slam your feet into it. Depending on the angle between you and the ramp, the speed, and probably how far into the wall you would have been placed on this tick, you can get almost catapulted into the air.
This, like many other techs, happens because your forward momentum gets transformed on impact. In this case it gets transformed into upwards momentum. Due to small differences in position having a butterfly effect on the outcome ramp jumps like curve boosts can appear to be almost completely RNG. I recommend praying to whatever higher deity you believe in before performing one.
Pros and Cons
Compared to the difficulty of this tech, the advantages are almost negligible. It is slightly faster than climbing a wall and preserves a bit of forward momentum. The biggest advantage is honestly the style points it adds to a rollout. See PlasmaNapkins “Overslide” and “Evergreen” for an example. In comparison, its major disadvantages of requiring special surfaces and being incredibly inconsistent firmly place it in the realm of “not usable outside of trick jumps.”
Tips
Like with ceiling boosts, a lot more edges than you might think have a small, curved part you can use to ramp jump. In addition you can ramp jump off other players heads.