Power over Ethernet (PoE) refers to a device that can receive power and exchange communication from a single ethernet cable. This means that the ethernet cable is used for both supplying power and completing data transmissions. This is pretty unique, as you normally wouldn't use the same cable for both of these tasks. But remember that there are several wires within a single ethernet cable. This is what makes this functionality possible.
The great thing about PoE is that using only one cable for both network and electrical power can help you achieve more flexible wiring setups. You only have to worry about running one cable instead of two. This can make it much easier to achieve the setup you want. In the case of a PoE cable, you will just have a cable running from your internet router to the camera. Depending on the location of the camera and the router, you may still need a professional to help you fish the wire through the walls. But this is still a relatively easy and straight forward setup.
Some cameras may need an additional piece of hardware to support PoE. This is what is referred to as a PoE injector. This device will "inject power" into the ethernet cable. The PoE injector will connect with a standard wall outlet for power. You will then connect an ethernet cable to the PoE injector from the internet router. A second ethernet cable will then run from the PoE injector to the camera. This really does not limit your wiring possibilities, as you just keep the PoE injector module right next to the router. Nothing will really change as a result. Also, not every PoE camera requires the use of a PoE injector.
When using a PoE camera, you must make sure tat the cabling you are using supports PoE technology. Not every ethernet cable can be used with a PoE wiring setup. For example CCA (copper clad aluminum) ethernet cables do not support PoE, and they cannot be used in this manner. Also make sure that the cameras themselves support PoE technology. Some cameras must be powered by conventional plug-in transformers. Although PoE is not possible with every setup, it can be really useful in certain situations.
Additionally, most PoE cameras can still be powered by conventional AC power if that is what you would prefer. Also you have to do is connect a compatible transformer from a wall outlet to the cameras. Then the camera will receive adequate power. The camera can then connect to the network using a hardwired ethernet connection or by using a wireless WIFI connection. Obviously, Power over Ethernet is only possible for cameras that use a hardwired ethernet connection. Cameras that communicate using WIFI will still need a cable for power. The only way a camera can truly be wireless is if it uses WIFI connectivity and battery power. There are some Arlo Cameras that support this type of setup.