ZigBee is an open global standard for wireless technology designed to use low-power digital radio (RF) signals for home automation. ZigBee operates on the IEEE 802.15.4 specification and is used to create networks that require a low data transfer rate, energy efficiency and secure networking. ZigBee uses the 900 MHz band in the US. This technology also has a low-channel bandwidth of 1MHz. It's restricted to wireless personal area networks (WPAN) and reaches an average 10 to 30 meters for usual applications.
ZigBee vs Z-Wave
ZigBee and Z-Wave are not compatible with each other. Zigbee operates on the 915 MHz frequency (in the US), Z-Wave operates at 908.42 MHz, meaning interference is minimal for Z-Wave and possible on Zigbee. Zigbee is faster with data rates at 40-250 kbps versus Z-Wave's 9.6-100kbps.
ZigBee can also support way, way more devices – 65,000+ devices, or nodes on the mesh network, in fact. Z-Wave on the other hand caps out at 232 devices, which is still plenty for most households.