Fess

In heraldry, a fess or fesse (from Middle English "fesse", from Old French, from Latin "fascia", "band") is a charge on a coat of arms (or flag) that takes the form of a band running horizontally across the centre of the shield. Writers disagree in how much of the shield's surface is to be covered by a fess or other ordinary, ranging from one-fifth to one-third. The "Oxford Guide to Heraldry" states that earlier writers including Leigh, Holme, and Guillim favour one-third, while later writers such as Edmondson favour one-fifth "on the grounds that a bend, pale, or chevron occupying one-third of the field makes the coat look clumsy and disagreeable." A fess is likely to be shown narrower if it is "uncharged", that is, if it does not have other charges placed on it, and/or if it is to be shown with charges above and below it; and shown wider if "charged". The fess or bar, termed "fasce" in French heraldry, should not be confused with "fasces".
Diminutives.
In English heraldry, two or more such charges appearing together on a shield are termed "bars", though there are no definitive rules setting the width of the fess, the bar, nor their comparative width. A shield of (often six or eight) horizontal stripes of alternating colour is called "barry". Narrower versions of the bar are called "barrulets" ("little bars"), and when a shield of horizontal stripes alternating colour is composed of ten or more stripes, it is called "barruly" or "burely" instead of "barry". A "cotise", defined as half the width of a barrulet, may be borne alongside a fess, and often two of these appear, one on either side of the fess. This is often termed "a fess cotised" (also "cottised", "coticed" or "cotticed"). Another diminutive of the fess called a "closet" is said to be between a bar and barrulet, but this is seldom found. A fess when "couped" ("cut off" at either end, and so not reaching the sides of the shield) can be called "humetty", but this term is very rare in the Anglophone heraldries and is most often used of the cross.
Other uses.
A shield "party per fess" (or simply "per fess") is divided in half horizontally ("in the manner of a fess"). A charge placed horizontally may be termed "fesswise" or "fessways", and two or more charges arranged in a horizontal row are blazoned "in fess" or "in bar".
Notable and unusual forms.
A "mural fess", that is a fess embattled and masoned of the field, can be seen in the arms of Suzanne Elizabeth Altvater.
The arms of Baroness Fritchie provide an example of "three Barrulets fracted and there conjoined to a Chevronel".
A flag which has a central "horizontal" stripe that is half the height of the flag is sometimes said to have a Spanish fess. The name is based on the most well-known example of this style of flag, the flag of Spain.