Hey there kiddo, have you ever seen a secret diary that your sister keeps, where she writes down everything she wants to keep private? Well, a code book is kind of like that diary for computer programs.
When computer programs are written, sometimes there are certain things that are meant to be kept secret or private, like passwords or special codes. Just like your sister writes down her secrets in her diary and locks it up, computer programs keep their secrets in a codebook.
The codebook is like a special book that only authorized people can access. They need to use a special key or code to open it up and read what's inside. Inside the codebook, there are instructions on how to use the secret bits of information that the program needs to run.
So, to sum it up, a codebook is a special book that keeps important secrets safe and protected, just like your sister's diary!