Plaque is a sticky layer of material containing germs that accumulates on teeth, including places where toothbrushes can't reach.  This can lead to gum disease.  The best way to get rid of plaque is to brush an flass your teeth carefully every day.  The toothbrush cleans the tops and sides of your teeth.  Dental floss cleans in between them.  Some people use waterpicks, but floss is the best choice.