1. playful or teasing
are you kidding?
The noun 'kidding' refers to something that is a playful or teasing action. As an adjective, it describes something playful, joking or deceptive. If you say you are 'just kidding' it means you are not being serious, you are joking. If you say 'you have got to be kidding' or 'are you kidding?', you are asking if someone is joking or being serious. This is an informal expression suited to social contexts.