Internet Protocol (IP) – a set of rules that dictate how data should be delivered over the public network (Internet). Often works in conjunction with the transmission control protocol (TCP), which divides traffic into packets for efficient transport through the Internet; together they are referred to as TCP/IP.
For example, when an email (using the simple mail transfer protocol – SMTP) is sent from an email server, the TCP layer in that server will divide the message up into multiple packets, number them and then forward them to the IP layer for transport. At the IP layer, each packet will be transported to the destination email server. While each packet is going to the same place, the route they take to get there may be different. When it arrives, the IP layer hands it back to the TCP layer, which reassembles the packets into the message and hands it to the email application, where it shows up in the Inbox.