Grades of Tea
Tea grading is based on the size of the leaf and types of leaves included in the tea. Though leaf size is an important quality factor, it is not, by itself, a guarantee of quality.

Teas are often designated as OP or FOP. These designations are part of the grading system used for whole leaf black teas and refer to the leaf size and amount of tip in the tea. Pekoe means teas picked as 2 leaves and a bud. OP, or Orange Pekoe, is a full-leaf tea with no tip or buds. FOP, or Flowery Orange Pekoe, is a longer leaf than an OP and has some buds. Grading systems and terminology vary with tea type and country. The system is especially highly developed for Indian teas (see the following table). But regardless of where the tea comes from, the more whole and less broken the leaf is, and the more buds it contains, the higher the grade of tea.

BLACK TEA LEAF GRADES
P:    Peko smaller, shorter leaves than OP
OP:    Orange Pekoe long, thin, tightly rolled leaves
FOP:    Flowery Orange Pekoe.  longer leaf than an OP but not as tightly rolled
GFOP:    Golden Flowery Orange Pekoe
FOP: with some golden tips    
TGFOP:Tippy Golden Flowery Orange Pekoe
GFOP: with more golden tips
FTGOP:   Finest Tippy Golden Flowery Orange Pekoe
BOP:    Broken Orange Pekoe    OP leaves that are broken
FBOP:   Flowery Broken Orange Pekoe
FOP: leaves that are broken    

GREEN TEA GRADES
There is no uniform grading system for green teas, but the better quality green consist of a leaf and bud, then 2 leaves and a bud and so on. Some common green tea leaf terms are:
Gunpowder: also called pearl tea, young leaves and buds are rolled tightly into pellets that unfurl in the cup
Imperial: loosely rolled pellets made from older leaves
Young Hyson: young leaves rolled long and thin