What is the "jump"/ Y axis? How It's called in scripting?

Hey, I'm a bit new in Unity and i really need help with something. I'm creating a simple game and i want to play an animation while I'm in air. It worked with Walking

             if(Input.GetAxis("Vertical"))
             {
             animation["Run"].wrapMode = WrapMode.Loop;
             AnimPlayer.animation.CrossFade("Run", 0.4);
             }
             else
             {
             animation["Idle"].wrapMode = WrapMode.Loop;
             AnimPlayer.animation.CrossFade("Idle", 0.4);
             }

^ That worked perfectly, but i need to know what Axis is for Y :(

I only found someone said about if(Input.GetAxis("Jump")) but that doesn't work :< Sorry for my bad english!