Meaning of polarization pulse in microwave (rotational) spectroscopy In the recent rotational spectroscopy literature, "microwave polarization pulse" is often used in conjuction with pulsed Fourier transform microwave spectroscopy (Google Scholar).

Sometimes the pulse angle is also mentioned such as $π/2$. I gather this term is similar to FT-NMR where the net magnetization vector is tipped at a certain angle. When we talk about microwave rotational spectroscopy, what is being polarized?

In other words, why do we call the microwave pulse as a polarizing pulse? I wanted to confirm that this is related to the net electric dipole moment vector of the molecules which is being oriented after excitation?
In NMR the sum of the magnetic dipole vectors is called the magnetisation, and this is induced in the sample by the large fixed external magnetic field acting on the nuclear spins. As you mention it is influenced, i.e. moved about,  by the magnetic field of the rf pulses applied to the sample and so ultimately cause the nmr signal. In optics the similar thing  can occur where an intense optical field can align the electric dipoles and cause a polarisation, i.e. macroscopic dipole in the sample, this is the optical equivalent of magnetisation. The experiment is far more difficult to do in optics, however, as the dephasing time (T2 time in nmr) is several orders of magnitude faster than in nmr as is the lifetime of any level optically excited. 

The field is generally called optical resonance spectroscopy and/or coherent transient spectroscopy with effects such as transient nutation, photon echos and self-induced transparency.