From Academic Kids
An ensign is a distinguishing token, emblem, badge, or flag such as a symbol of office. The word is derived from the French enseigne from the Latin plural insignia and is more particularly used of a military or naval standard or banner. An armorial ensign applies specifically to heraldic symbols of an army.
In nautical use, an ensign in the form of a flag is usually flown at the stern of a ship or boat to indicate its nationality. Ensigns may also be flown from the gaff of a ship, and may be shifted to the yardarm when the ship is underway.
In some countries, such as the United States of America and France, the national ensign is identical to the national flag, while in others, such as the United Kingdom and Japan, there are special national flags for maritime use.
In heraldry, an ensign is the ornament or sign, such as the crown, coronet or mitre, borne above the charge or arms.