UWB is a broad category of radio technologies that transmit simultaneously over a very large range of radio frequencies. While "wide-band" technologies typically transmit over a frequency range spanning around 5 MHz, a UWB transmission may span up to 500 MHz.
Because a UWB signal is spread out over such a wide range of frequencies, a useful signal can be transmitted in whole, while the signal at any one frequency is almost non-existent. In this way UWB can share spectrum with other radio technologies. When properly regulated and implemented, interference is minimal between UWB and other radio systems in overlapping frequency bands.
UWB can be used for RADAR, but more recently has attracted attention for high-speed, short-range data transmission.
A version of Bluetooth is planned that will use UWB for just such high-speed, short-range applications.