delusions refer to disturbances in thinking involving disordered thought content and strong beliefs that are misrepresentations of reality.
Other /More definition:
Delusions refer to beliefs that other people regard as unfounded, such as the belief that one is being severely persecuted; fixed false beliefs with no basis in reality and not consistent with the person's intelligence or cultural background; beliefs that are contrary to reality and are firmly held despite evidence that they are inaccurate. Delusions, moreover, are disturbances in thinking involving disordered thought content and strong beliefs that are misrepresentations of reality.