Raspberry Pi HATs are electronic boards similar to Arduino shields. Like shields, HATs are designed suitable for Raspberry Pi pinout and it is enough to stack the HAT over the Raspberry Pi connect them. HAT stands for “Hardware on top”, so HATs are addons that are attached on top of Raspberry Pis.
There are some specifications determined by the Raspberry Pi Foundation for classifying an add-on board as a Raspberry Pi HAT. These specifications are;
An addon that does not meet this specifications can still be used with a Raspberry Pi, but it cannot be called a Raspberry Pi HAT.