Thumb twiddling is an activity that is done with the hands of an individual whereby the finger

Finger

A finger is a limb of the human body and a type of digit, an organ of manipulation and sensation found in the hands of humans and other primates....

s are interlocked and the thumb

Thumb

The thumb is the first digit of the hand. When a person is standing in the medical anatomical position , the thumb is the lateral-most digit...

s circle around a common focal point, usually in the middle of the distance between the two thumbs.

While it is an expression of at least a moderate amount of manual dexterity, thumb twiddling is frequently used as an example of a useless, time-wasting activity. It is equated with other activities that are also considered useless by the speaker. Therefore it is most often used as a synonym for an activity that will take the attention of the performer, but will not yield any useful results.

Thumb twiddling can be seen as an expression of which hand is dominant

Laterality

Laterality is the preference that most humans show for one side of their body over the other. Examples include right-handedness or left-footedness. It may also apply to other animals, or to plants.- Human laterality :...

 with the individual. The weaker handed thumb will follow the dominant handed thumb in the activity.

Obsessive-compulsive behavior

Thumb twiddling can start out as an innocent activity, but can become a problem if the individual performs this activity to excess. Excessive demonstration of this activity may actually be evidence of a mental or neurological problem. Excessive thumb twiddling may be one of many symptoms of an obsessive-compulsive disorder

Obsessive-compulsive disorder

Obsessive–compulsive disorder is an anxiety disorder characterized by intrusive thoughts that produce uneasiness, apprehension, fear, or worry, by repetitive behaviors aimed at reducing the associated anxiety, or by a combination of such obsessions and compulsions...

.