What is A-BFT (Associated Beamforming training Time)?

As the low-frequency bands become very much crowded, mmWaves or mmWave communications have gained attention. It adopts beamforming technology that can basically generate directional beams to compensate for path losses in the medium. In the Association beamforming training (A-BFT) phase of the beamforming training, a station randomly selects a slot to use for the opportunity. This is known as Associated Beamforming training time.