It was a new one for me this morning - and I don't like falling behind the curve on new technology - so I took a few minutes to learn something new:
Beamforming is a specialized method of antenna-based RF transmission. Essentially is has to do with selectively using/timing different antennas or frequency bands in order to aim the transmission/reception either physically or virtually at the source/target you are most interested in.
This is different from the concept of omni-directional transmission/reception that most of us are familiar with. You can think of it in a way as the concept of a satellite dish pointing at a fixed location instead of a pair of rabbit-ears trying to listen to everywhere at once. Only in this case - the dish would be self-aiming.
Originally developed for sonar applications - it found another application in cellular networks and is now being introduced for wireless networking. Expect to hear more of this buzzword in the near future.