Terms and definitions
Dry contact - slang term in the field of industrial automation and signaling, denoting a discrete output signal of the device.
The word dry means that there is no voltage on the dry contact terminals unless the terminals are connected to other equipment.
Normally open contact.
Normally closed contact.
A group of 3 contacts that can be in two states: open and closed.
Passive PoE (Power over Ethernet) is a technology that allows you to transmit power over an Ethernet cable.
Pins 4, 5 (+) and 7, 8 (-) of the Ethernet RJ45 connector are used for power.
You can read more about how it works in the article Wiki Passive PoE.