mark, symbol, signal; flag, standard, pennant), from Latin insignia (plural)) is a junior rank of a commissioned officer in the armed forces of some countries, normally in the infantry or navy.

In Thomas Venn's 1672 Military and Maritime Discipline in Three Books, the duties of ensigns are to include not only carrying the colour but assisting the captain and lieutenant of a company and in their absence, have their authority.

The Spanish alférez and Portuguese alferes is a junior officer rank below lieutenant associated with carrying the flag, and so is often translated as "ensign".

In the Canadian Army, Ensign (Enseigne) is the distinctive rank for Second-Lieutenant in the Guards Regiments.

During the Ancien Régime in France, as in other countries, the ensign (enseigne) was the banner of an infantry regiment.

It was briefly renamed ship-of-the-line sub-lieutenant (sous-lieutenant de vaisseau) in the end of the 18th century, but its original name was soon restored.

Another was that, at the time, New Zealand was actively involved with the United States Armed Forces, so it made sense to balance the rank system out with that used by the United States Navy.Until 1871, when it was replaced by second lieutenant, ensign was the lowest rank of commissioned officer in infantry regiments of the British Army (except fusilier and rifle regiments, and the Marines, which always used second lieutenant).

Today, the term "ensign" is still used by the Foot Guards regiments, for instance during the ceremony of trooping the colour.

[6]: 560  The act of March 3, 1791 added a second regiment to the Army strength, doubling the total number of ensigns.

[9] Prospective Naval Aviators and Naval Flight Officers have a 12 to 18 month flight training track to earn their wings, followed by a six to nine-month training track in a Fleet Replacement Squadron before being assigned to fly combat aircraft in a deployable Fleet aviation squadron.

Navy and Coast Guard ensigns wear collar insignia of a single gold bar and because of this share the nickname "butterbars" with Army, Air Force, Space Force, and Marine Corps second lieutenants, who wear the same insignia.

In the United States Public Health Service Commissioned Corps – a uniformed service in the United States Public Health Service — those wearing the rank of ensign are part of a commissioned officer student training, and extern program (COSTEP), either junior, for those with more than a year remaining of education in a commissionable degree (JRCOSTEP), or senior, for those within one year of graduating with a commissionable degree (SRCOSTEP).