XBee & ZigBee

What is the difference between XBee and ZigBee? I dont get it. When I search for ZigBee modules all I see is XBee modules.

Xbee is the name for several types of radio transceiver hardware made by the Digi company.

Zigbee is a 'mesh' messaging protocol. You often see it mentioned in the context of battery powered sensors used in home automation systems.
Some Xbee devices support Zigbee communication and several other companies make Zigbee compatible devices.