What is the definition or description of: arm swelling?

Could be infection: Swelling of the arm could be due to allergy, infection, poor circulation or lymphadema where the lymphatic drainage is blocked. If you have swelling you should see your doctor.

Not to be flippant..: Really all one could say is swelling (medically known as edema) of the arm, from shoulder to wrist. Any more information forthcoming from a doctor, would be due to a more informative question.