The relay module, as expected, is connected to the standard Grove interface, but it is classified as an actuator because it does not provide readings.

Other actuator modules such as LEDs, displays, motor drivers, and buzzers are used to perform actions instead of reading states. The relay module too has two states, open circuit or closed circuit, meaning that the input connection of the relay is not connected to the output.  

This concludes our review of the parts. Let's move on to the next step in the solution development process.