An **ensign** is the national flag flown by a vessel at sea, or by a military formation, to identify its nationality or allegiance. Many states maintain separate civil, state and naval ensigns, distinguished by colour or by the presence of a defacement. The position at which an ensign is flown is fixed by long custom: at the stern when in harbour, at the gaff when under way.
**Example**: The White Ensign is flown by ships of the Royal Navy, the Red Ensign by British-registered merchant vessels.
**See also**: [jack](/glossary/jack/), [defacement](/glossary/defacement/), [courtesy-flag](/glossary/courtesy-flag/), [ensign-at-sea](/glossary/ensign-at-sea/)