HAT stands for “Hardware attached on top”. It is a new hardware specification for add-one modules for the new Raspberry Pi model B+. HATs have several advantages compared to older add-on modules for the Raspberry Pi.
The Raspberry Pi PoE HAT powers a Raspberry Pi 4 Model B and Raspberry Pi 3 Model B+ via an Ethernet cable.
Power-sourcing equipment is required on the Ethernet network.