Tic

A tic is a sudden and repetitive motor movement or vocalization that is not rhythmic and involves discrete muscle groups. It is typically brief, and may resemble a normal behavioral characteristic or gesture.

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.

Tics must be distinguished from movements of disorders such as chorea, dystonia and myoclonus; the compulsions of obsessive–compulsive disorder (OCD) and seizure activity; and movements exhibited in stereotypic movement disorder or among autistic people (also known as stimming).