A fleur-de-lis is an abstract representation of a lily or an iris flower. It's hard to describe in words, so look at the picture. The plural is fleurs-de-lis, and a semy of them would be fleury-de-lis . There are some edge-treatments, where the edges of lines of divisions are shaped like fleurs-de-lis, or perhaps the ends of a cross. In that case, the terms Fleury (flory) or Fleuretty are used. There are some technical differences between these uses, but I won't get into them here.

a stylized version of the iris flower. Used often in heraldry and French designs.

A symmetrical symbol that was originally French and means "flower of the lily". The symbol is popularly used in fashion jewelry designs and in the US is adopted by Louisiana and the city of New Orleans.

The fleur de lis (meaning "flower of the lily" in French) is a heraldic symbol of French royalty; it is still used in many French flags. Fleurs de lis are a motif often used in jewelry. The green enamel fleur de lis pin above is by Trifari.