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. 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). From Wikipedia