According to Webster's Revised Unabridged Dictionary, gyron, in the language of heraldry, is:
"A subordinary of triangular form having one of its angles at the fess point and the opposite side at the edge of the escutcheon. When there is only one gyron on the shield it is bounded by two lines drawn from the fess point, one horizontally to the dexter side, and one to the dexter chief corner."
In the language of more common English, that means a right-angled triangle in the top-left quarter of a shield, with its point in the centre of a shield.1
Now, the next really useful word to add to our vocabulary is gryonny. This is where we have more than one gyron. You can have as many gyrons as you wish (nobody will stop you). The dartboard, for example, has ten gyrons, and the shield beneath the dartboard shows four.
Four gryons form the centre of a Gyronny Cross (French: Croix Gironée). Extending the halves of neighbouring gryons horizontally and vertically, results in a cross which gives a somewhat 3-dimensional appearance. (See the Eastern Orthodox Cross is and other 3-D crosses.)
The Fitched Gyronny Cross, shown on the left, was kindly drawn for us by JS, an aeronautical engineer. (Click the image for a larger view.)
Perhaps more than any other drawing on this page, the Fitched Gyronny Cross has a three-dimensional appearance. As such, this form is often used to depict the Star of Bethlehem at Christmas.
The Gyronny Cross is found in several family coats of arms. It is a cross adorned with the corporate colours (black and white) used by the Ordo Praedicatorum (Order of Preachers), also known as the Dominicans. (See Dominican Cross)
Another good example of a Gyronny Cross can be seen on the municipal flag of Covilhã, central Portugal.
The US Maryland State flag shows two such crosses, although strictly speaking, since the centres of the red and white crosses do not conform to the required triangular shape, giving them the illusion of depth, this cross is more accurately described as a Botonée Cross countersigned. But whether this is called a Gyronny or a countersigned Botonée cross, doesn't really matter. As with all crosses, there is a deeper meaning than whatever is implied by its name.
This red and white cross was the coat of arms for the Crossland aristocrats in England, whose descendant, the English politician and coloniser George Calvert, sought a royal charter to settle the region of Maryland. His grandson, Leonard Calvert, became the first colonial governor of the state and his great-grandson, Cecil Calvert, became the first Proprietor of the colony. This led to the inclusion of the Crossland emblem in the Maryland flag in 1904. It is the only state flag in the US which is based on a British heraldic emblem.
Red and white happened to be 'secession colours', hence this cross became the banner for Confederate supporters in Maryland.