The difference in practice
A PoE camera receives power and network via one network cable. That cable runs to a PoE switch or recorder. This ensures the camera has a permanent connection and you don't need to attach a separate adapter to the camera. For permanent security, that is usually the most reliable solution.
A wifi camera uses a wireless network, but usually still needs power. This sometimes makes installation easier, but it doesn't solve everything. You still need to think about power supply, range, walls, distance from the router and what happens if the wifi network is crowded or unstable.

