Z-Wave is a wireless protocol for controlling and monitoring devices designed for homes. While similar to more familiar wireless types like WiFi or Bluetooth, Z-Wave is designed to require very little energy, which means that Z-Wave devices can operate on battery power for 1-3 years.
Z-Wave devices use something called "mesh networking" for communications. This means that some Z-Wave devices can amplify the radio signal by passing it along. For example, a garage door opener at the perimeter of your home can connect to the gateway by letting a smart plug pass the signal along.
Z-Wave operates in the sub-gigahertz band(868.4 to 956MHz depending on region), and does not cause interference with Wi-Fi and other wireless technologies in the 2.4-GHz range.
For more detailed information, please visit the Z-Wave Alliance website.