Internet Protocol is the protocol the Internet is built on. It was developed by a Department of Defense (DOD) research project to connect a number of different networks designed by different vendors into a network of networks (the "Internet").
You may have heard of TCP/IP; this is TransmissionControlProtocol used on top of IP. Think of it as a layer system - TCP takes IP and adds useful stuff to it.
IP is responsible for moving packet of data from node to node. IP forwards each packet based on a four byte destination address (the IP number). The Internet authorities assign ranges of numbers to different organizations. The organizations assign groups of their numbers to departments. IP operates on gateway machines that move data from department to organization to region and then around the world.
IP is defined in RFC 791.
An IPv4 (version 4) address looks like 220.127.116.11; version 4 is in current usage. A push to move to Version 6 (IPv6) is in place due to the number of IP addresses in v4 being scarce in places: an IPv6 address looks like 3ffe:0501:0008::0260:97ff:fe40:bade and offers something like millions of possible IP addresses per square foot of the planet.
Go away and read about IP and then take an Internet Protocol quiz.