A Tijuana Bible is like a little booklet with cartoons inside that grown-ups would read. These booklets were really popular a long time ago, in the 1920s and 1930s. They were often printed in Tijuana, which is a city in Mexico that's across the border from the United States.
The cartoons inside these booklets were often very naughty, which means they had things in them that kids aren't supposed to see or hear. They usually featured popular characters from movies or comics doing things that they wouldn't normally do, like having naughty conversations or doing rude things.
People would read these Tijuana Bibles in secret because they were considered very inappropriate. They weren't something that kids were allowed to see or read, and sometimes even adults weren't supposed to read them!
Today, Tijuana Bibles are mostly just collected by people who like to study old cartoons and comic books. They're still considered a bit too grown-up for most people, but they're an interesting part of the history of comics and cartoons.