The IP address is a unique string of numbers used to identify each computer connected to the internet. You can think about it as your physical home address, where letters can be sent to you, or when you send a letter you have to put your address on it as the sender. The IP is used when your computer communicates through the internet back and forth. Usually, each set of IP address is associated with a country, state, and zip code, therefore it can be easy to find out where a person is based on their IP.
IP is widely used by many companies for different reasons, one of which is content blocking. For example, if you decided to watch Netflix while you were traveling overseas, you might not be able to find your favorite show due to copyrights and licensing. YouTube does the same thing for some of its content. Of course, the IP address can be used for different things such as ads targeting, but the technology of content blocking and ad targeting is pretty much the same.
Examples of IP address: