IP camera can also be used as a webcam but IP camera is more advanced
A USB webcam is a camera that connects to a computer, usually through plugging it in to a USB port on the machine.
IP camera connects directly to your network router in the conventional wired way using cable or some models also have a wireless connection.
This type of webcam does not need a computer to connect to the Internet as it has all the electronics needed for this built in. This makes the camera very reliable as there is no PC involved or separate operating system, just its own embedded program which is usually Linux based.