Stereotypy:

Wikipedia:

"A stereotypy is a repetitive or ritualistic movement, posture, or utterance. Stereotypies may be simple movements such as body rocking, or complex, such as self-caressing, crossing and uncrossing of legs, and marching in place. They are found in people with intellectual disabilities, autism spectrum disorders, tardive dyskinesia and stereotypic movement disorder, but may also be encountered in neurotypical individuals as well."

Proposed causes:

"There are several possible explanations for stereotypy, and different stereotyped behaviors may have different explanations. A popular explanation is stimming, which hypothesizes that a particular stereotyped behavior has a function related to sensory input."

[See also: Stereotypies]