LTE-U stand for LTE - unlicensed spectrum. It was originally developed by Qualcomm, for the use of the 4G LTE radio communications technology in unlicensed spectrum, such as the 5 GHz band used by dual-band Wi-Fi equipment.
LTE-U would allow cellphone carriers to boost coverage in their cellular networks, by using the unlicensed 5 GHz band already populated by Wi-Fi devices. While cell providers ordinarily rely on the radio spectrum to which they have exclusive licenses, LTE-U would share space with Wi-Fi equipment already inhabiting that band – smartphones, laptops and tablets connecting to home broadband networks, free hotspots provided by businesses, and so on.
References -
https://www.qualcomm.com/invention/technologies/lte/unlicensed
https://en.wikipedia.org/wiki/LTE_in_unlicensed_spectrum
