IrDA is/was a protocol for short range, infrared device communication. At the time, WIFI was far less common. Bluetooth was nonexistent. Palm devices had IrDA ports; so did several printers. The HP 5M laserprinter comes to mind: I used to use IrDA to print from both a Palm device and a Pismo.
I don't know of anything that is using it now but I suppose it could be used for legacy devices such as printers from the same time period as your G3.