It’s a home automation protocol, like X10. You buy devices that can talk ZigBee to a hub device (probably can use a computer on your local network for this). From the hub you can do all the usual automation tasks.
The bigger hassle seems to be different zigbee hubs that have varying levels of compatibility, so while you can pair the devices you can't get the data you want.
I've just been down the research rabbit hole, and about to try using zigbee2mqtt to bypass this nonsense (this also then means the only internet connectivity will be through a device you control)
Philips Hue hub talks to diagnostics.meethue.com all the time, and it gets kind of annoying already in the pihole stats.