Flossing is a way of removing debris and bacteria that your toothbrush cannot reach. Floss is a thin cord or string made out of synthetic material that is inserted in between two adjoining teeth. This thin cord is moved up and down in between the teeth to remove food particles and bacteria.
Floss removes debris and plaque that stick to the gums and teeth. Another benefit of flossing is it stimulates blood circulation of the gums. According to many dentists, flossing is the most important tool for fighting plaque. Once your baby’s teeth are fully erupted, it is never too soon to begin flossing their teeth. Flossing daily is an excellent proven method for preventing dental problems. Brushing and flossing your child’s teeth should be a daily routing to prevent dental problems later in life such as cavities, periodontal disease, and other problems.
 http://kb-dental.com/patient-education/dental-care/flossing, accessed December 22, 2011