Terefah is a Hebrew word that means something is not kosher or not allowed to be eaten according to Jewish dietary laws.
Think of it like a game of food rules. Some foods are allowed and some are not. Just like some toys are allowed to be played with and some are not.
To be considered kosher (or allowed), an animal must meet certain rules. The animal must have split hooves and chew its cud. So, cows, sheep, and goats are kosher, but pigs are not because even though they have split hooves, they do not chew their cud.
If an animal has something wrong with it internally, like a hole in the lung or an injury in its digestive system, it is called terefah and is not kosher. Just like how if you have a toy that is broken, you can't play with it anymore.
So, terefah means that something is not kosher because of something that is wrong with it inside. And just like how we have rules for toys, Jewish dietary laws have rules for what can and can't be eaten.