Paranoia is a mental health condition that affects a person's thoughts. A person with paranoia is called paranoid. Paranoia is a thought process heavily influenced by anxiety or fear, often to the point of irrationality and delusion.
A paranoid person's thinking is shaped by fear and anxiety. For example, the person may fear that other people are "out to get them" or are planning to hurt them. They may believe that video cameras are watching them, or that a certain group (like the police or CIA) is following them. They may also believe that other people can control their thoughts or use magic to hurt them. Even if these fears seem strange or absurd to others, they feel very real to the person with paranoia. They truly believe that they are in danger.