The Definition of Heraldry according to Wikipaedia:
Heraldry is the profession, study, or art of devising, granting, and blazoning arms and ruling on questions of rank or protocol, as exercised by an officer of arms. Heraldry comes from Anglo-Norman herald, from the Germanic compound *harja-waldaz, “army commander”. The word, in its most general sense, encompasses all matters relating to the duties and responsibilities of officers of arms. To most, though, heraldry is the practice of designing, displaying, describing, and recording coats of arms and heraldic badges.
Historically, it has been variously described as “the shorthand of history” and “the floral border in the garden of history.” The origins of heraldry lie in the need to distinguish participants in combat when their faces were hidden by iron and steel helmets. Eventually a formal system of rules developed into ever more complex forms of heraldry.
The system of blazoning arms that is used in English-speaking countries today was developed by the officers of arms in the Middle Ages. This includes a stylized description of the escutcheon (shield), the crest, and, if present, supporters, mottoes, and other insignia. Certain rules apply, such as the Rule of tincture. A thorough understanding of these rules is a key to the art of heraldry. The rules and terminology differ from country to country; indeed several national styles had developed by the end of the Middle Ages, but there are some aspects that carry over internationally.
Though heraldry is nearly 900 years old, it is still very much in use. Many cities and towns in Europe and around the world still make use of arms. Personal heraldry, both legally protected and lawfully assumed, has continued to be used around the world. Heraldic societies exist to promote education and understanding about the subject.