External displays can be connected to an Android device in different ways, e.g. via a HDMI cable. Best examples are obviously TV devices, but it could as well be a computer monitor.
There are multiple ways to connect an external display to your Android device. This external display either mirrors the content of the screen which is integrated with the Android device (most common use), or might even show different content streamed from it.
Some ways to connect an external display include: