Tic
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.
Tic disorder
Tic disorders is defined in the "Diagnostic and Statistical Manual of Mental Disorders" (DSM) based on type (motor or phonic) and duration of tics (sudden, rapid, nonrhythmic movements). Tic disorders are defined similarly by the World Health Organization (ICD-10 codes).