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.
see Tic convulsif
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.