A word derived from the Latin arma, which signifies in heraldry a mark of honor, serving to 
distinguish states, cities, families, etc.
Arms are the ensigns armorial of a family, consisting of figures and colours borne in shields and banners as marks of dignity and distinction, and descending from father to son.
My main example of this would be the Royalty of England. You can see how the shield change over time, but they keep the symbols of the family lines as well.