Dear @Kashyap.Subham,
The units as stated in Nm^2 are correct. These are cross-section stiffness values, e.g., as discussed in the following forum topic: FlpStff and EdgStff - #2 by Jason.Jonkman.
In FAST v7, the elastic axis and mass axis of the undeflected blade are aligned with the pitch axis, while the aerodynamic center may be offset from the pitch axis. The offset of the aerodynamic center from the pitch axis acts as a moment arm so that the aerodynamic loads applied at the aerodynamic center can generate pitching moments. Moreover, when the blade deflects flapwise, any force in the edgewise direction will create a pitching moment because the flapwise deflection acts as a moment arm; likewise, when the blade deflects edgewise, any force in the flapwise direction will create a pitching moment.
Best regards,