A tic is a sudden, repetitive, nonrhythmic motor movement or vocalization involving discrete muscle groups.
Tics can be invisible to the observer, such as abdominal tensing or toe crunching. Common motor and phonic tics are, respectively, eye blinking and throat clearing.
The Yale Global Tic Severity Scale (YGTSS) is a clinician-rated instrument considered the gold standard for assessing tics in patients with Tourette's Syndrome and other tic disorders. Previous psychometric investigations of the YGTSS exhibit different limitations such as small sample sizes and insufficient methods
Tics must be distinguished from movements of other movement disorders such as chorea, dystonia, myoclonus; movements exhibited in stereotypic movement disorder or some autistic people, and the compulsions of obsessive–compulsive disorder (OCD) and seizure activity.
Tic: can be suppressed, is not repetitive (if repetitive, may be hemifacial spasm).
see Tic convulsif