The following rotational convention is used for both Nodal Coordinate Systems Results and Elemental Coordinate Systems Results:
The first rotation is called ... Euler XY and is in the X-Y plane (X towards Y, about Z).
The second rotation is called ... Euler YZ and is in Y1-Z1 plane (Y1 towards Z1, about X1).
The third rotation is called ... Euler XZ and is in X2-Z2 plane (Z2 towards X2, about Y2).
X1, Y1, and Z1 refer to the coordinate system axes after the initial rotation about the global Z axis.
X2, Y2, and Z2 refer to the coordinate system axes after the initial rotation about the global Z axis and subsequent rotation about X1.
See Figure 3.2: Euler Rotation Angles from the Modeling and Meshing Guide for a pictorial representation of this convention.