Plugboard

Imagine you have a box with lots of switches in it. Each switch can be turned on or off. When you turn on a switch, it connects two letters on the box. For example, if you turn on switch 1, it connects the letter A to the letter R. If you turn on switch 2, it connects the letter B to the letter J. This box is called a plugboard.

Now, let's say you want to send a secret message using a special code. You use the plugboard to change some of the letters in your message. For example, if you turn on switch 1, you can change all the A's in your message to R's. If you turn on switch 2, you can change all the B's in your message to J's.

This makes it harder for people who might intercept your message to read it. They might know your secret code, but they won't know which letters you changed using the plugboard.

The plugboard was used in old-fashioned machines called Enigma machines, which were used during World War II to send secret messages.