I.e., the y value of the point on the surface that your avatar is standing on.

Using the default “being of light” avatar, MyAvatar.getJointPosition(“LeftFoot”).y gives a y value that is 0.111m too high. MyAvatar.getJointPosition(“LeftToeBase”).y gives a y value that is 0.014m too high. And MyAvatar.getJointPosition(“LeftToeEnd”).y gives a y value of 0.0 (i.e., joint not present in skeleton).