A metacognition has sometimes been described as a 'thought about a thought'. Formally they are defined as beliefs about thoughts. Hence appraisal of a thought is influenced by positive or negative beliefs which follow on from the initial cognition. Examples of metacognitive beliefs include metaworry (worry about worry), thought-action fusion (the belief that a thought automatically predicts an outcome), cognitive confidence (beliefs about cognitive ability) and negative beliefs about the controllability of thoughts.
Considerable research has been carried out on generalised anxiety and Obsessive Compulsive Disorder by authors such as Adrian Wells of Manchester University in England. Wells (1995, 2005) suggests that metaworry (a metacognition) differentiates those with generalised anxiety from 'normals'.
Wells, A. (1995). Metacognition and worry: a cognitive model of generalised anxiety disorder. Behavioural and Cognitive Psychotherapy. 23, 301-320
Wells, A. (2005). The metacognitive model of GAD: Assessment of metaworry and relationship with DSM-IV generalised anxiety disorder. Cognitive Therapy and Research. 29(1). 107-121.