ELI5: Explain Like I'm 5

Trench code

Trench code is a special way of writing secret messages. It was used during World War I by soldiers in the trenches. To write a trench code, the writer would make lines in the dirt. The lines each stood for a different letter of the alphabet. For example, one line may stand for the letter 'A', two lines for the letter 'B', and so on. To decode the message, the reader would count the lines and figure out which letter each line stands for. It was a quick way to send secret messages from one soldier to another, or from one side of the trenches to the other.