Massive MIMO refers to the use of a large number of service antennas operating coherently and adaptively, to significantly augment the bandwidth in mobile networks, as opposed to the conventional point-to-point MIMO.
The large number of antennas focus the transmission and reception of signal-energy into much smaller regions of space, bringing huge improvements in throughput and energy efficiency, particularly when combined with simultaneous scheduling of a large number of user terminals (e.g., tens or hundreds).