Okay, so you know how sometimes people send secret messages to each other? Well, sometimes those messages are sent by important people who work for the government. These messages are called diplomatic cables.
Now, a few years ago, someone leaked a whole bunch of these diplomatic cables to a website called Wikileaks. This was a big problem because the messages were not supposed to be seen by anyone except the people they were meant for.
The leaked cables had information about things like secret meetings between important people from different countries, and private opinions that those officials had about each other. Some of the things said in these cables were not very nice, and some people were upset that they had been made public.
The United States government was especially concerned about this leak because it made them look bad in some ways. They were worried that other countries might not want to work with them in the future if they thought that their private conversations could be made public.
So, the diplomatic cables leak was a big deal because it involved secret messages that were not supposed to be seen by anyone outside of the people they were meant for, and it caused some pretty serious problems for the United States and other countries involved.