To fidget is to make little movements with your hands and feet. Even if you're nervous during your job interview, try not to fidget.
The word fidget is related to the Old Norse fikja, meaning "move briskly, be restless or eager." If you are feeling impatient or anxious you might fidget in your seat or fidget with a pen in your hands. A person who fidgets a lot can be referred to as a fidget and so can that quick anxious movement itself.