Unity, huh, how?
Quaternion.identityIdentity is the zero rotation. (0, 0, 0, 1).
Vector3.zero, (0, 0, 0) in Euler angles.
When used as a local orientation the target will be oriented identically to its parent.
When used as a global orientation the target will be perfectly aligned with the world space axes.
Return to Quaternions.
Next, Quaternion.Euler.