Gaffing is when you use something to trick or fool someone. It's kind of like playing a prank or a joke on someone.
Imagine you have a toy spider and you want to scare your friend. You could use the toy spider to gaff them. You might hide it in their backpack or put it on their chair so that when they see it, they get a surprise and maybe even scream a little. That's gaffing!
Gaffing is not meant to hurt or make someone feel bad. It's all in good fun and it's important to only gaff people who you know will enjoy it. If someone doesn't like being gaffed, it's always best to stop and apologize, because nobody likes to feel scared or embarrassed.