This is a PoE splitter / converter that:
Input: 48V PoE (from a PoE switch or injector, IEEE 802.3af/at)
Output: 24V passive PoE (via RJ45)
Power: up to 24W (24V / 1A)
In simple terms:
It lets you power 24V passive devices using a standard 48V PoE network.