The Wikipedia article https://en.wikipedia.org/wiki/Dark_mattersays DASI first detected the CMB polarization, and CBI provided the first E-mode polarization spectrum with compelling evidence that it is out of phase with the T-mode spectrum.A footnote  leads to https://arxiv.org/abs/astro-ph/0409569which says Ground-based interferometers provided fluctuation measurements with higher accuracy, including the Very Small Array, the Degree Angular Scale Interferometer (DASI) and the Cosmic Background Imager (CBI). DASI first detected the CMB polarization, and CBI provided the first E-mode polarization spectrum with compelling evidence that it is out of phase with the T-mode spectrum.Another Wikipedia article https://en.wikipedia.org/wiki/Cosmic_microwave_background#Polarizationsays E-modes E-modes were first seen in 2002 by the Degree Angular Scale Interferometer (DASI). B-modes Cosmologists predict two types of B-modes, the first generated during cosmic inflation shortly after the big bang, and the second generated by gravitational lensing at later times. I was able to find some discussions about E-mode, M-mode, and B-mode, but nothing about T-mode. I would appreciate any information which would help me understand what T-mode polarization is.