The 'nothing-to-hide argument' is something people say when they think privacy laws aren't important, because they have nothing to hide. It means that a person believes they don't have any secrets, so they don't need to worry about privacy or be protected by laws.
People with this argument think that since they don't have anything important to hide, it's alright for other people to know about them and their life. They don't think things like their location, what they search on the internet, what they buy, and their emails should be private.
Even though it might feel like no one needs privacy if they don't have anything to hide, that isn't always the case. Everyone has a right to privacy, not just people who have secrets. Privacy is about making sure that people can keep their information and choices safe and private, even if they don't have secrets.