Wavedashing is an advanced technique that can be pulled off in Rivals of Aether and was named after the Melee and Tekken technique of the same idea.
In Super Smash Bros Melee, Wavedashing was executed by air dodging into the ground and was a unique movement option that allowed the player to use any grounded option afterwards. The same holds true for Rivals of Aether.
In Rivals of Aether, the wavedash can easily be executed by holding either horizontal direction, and then pressing the jump and dodge button simutaneously. (Jump should still be pressed first, otherwise you will just roll.) It is very useful for moving around. However, you are extremely vulnerable while using it.
Wavelanding is also an advanced technique in Super Smash Bros Melee, and is very similar to how a wavedash works, but is used for different purposes. A waveland is executed by air-dodging into the ground before landing. It is useful for going through platforms faster or throwing off your opponent.