Stereotypic Movement Disorder (SMD) is a neurological disorder that is characterized by repetitive, non-functional motor behaviors, such as body rocking, hand flapping, or head banging. People with SMD may engage in these behaviors for hours at a time, without any apparent purpose or goal. However, there are several synonyms or related terms that are used to describe this disorder, such as stereotypies, stereotypic movements, or repetitive motor behaviors. These terms emphasize the repetitive nature of the disorder, and may be used interchangeably with SMD. Other related terms include tics (involuntary, rapid motor movements), compulsions (repetitive, ritualistic behavior), and perseveration (repetitive, persistent behavior). All of these terms describe disorders that involve repetitive or compulsive behaviors, and may share some underlying neurological or psychological features.