Let's say Alice is writing Bob a letter, but Bob's postal slot is only big enough for a small index card-sized envelope. Rather than writing her letter on regular paper and then trying to cram it through the postal slot, Alice splits her letter into much smaller portions, each of which is only a few words long, and writes these sections on index cards. She hands the stack of cards to Bob, who arranges them so that he can read the entire message.

This is similar to how Internet packets work. Assume a user requires the loading of an image. The picture file does not travel in one piece from the webserver to the user's machine. Instead, it's broken down into data packets, transported across the Internet's lines, cables, and radio waves, and then reassembled into the original photo by the user's computer.