Fancy Shape are any shape except rounds. A pear shape is an example of a fancy shape. Sometimes fancy shapes are simply called fancies. Feathers are cracks of various sizes. Normally, these do not weaken the diamond and can be difficult to see if small and oriented vertically.
Fire is the colored light reflected from within a diamond through the crown.
Fire is maximized by cutting a diamond to the correct proportions. GIA refers to the Gemological Institute of America, an independent, non-profit organization which sets and upholds standards for grading diamonds and other precious stones. Girdle is the narrow rim around the diamond. The girdle plane is parallel to the table and is the largest diameter of any part of the stone. Head is the part of a ring that contains the prongs which hold a diamond in its setting.