Interestingly, in Japan, teas are not graded by size of leaf. Most Japanese teas are blended in their final stage of production. Several lots of varying sizes are mixed for cup consistency.
Taiwan is the only major tea producer which actually grades its tea on flavour as well as its look or appearance. This used to be a government-run operation, but that was ended some years ago. Still, the system worked so well for the farmers and buyers of the tea that it is carried out the same way by citizens to this day. Taiwan holds regional tea competitions and the scoring breakdown - 20% aroma, 20% dry leaf appearance and 60% flavor - is also used in formal grading. Gold-medal-winning oolongs can sell for sky-high prices; the Taiwanese take their oolong very seriously.
You may still see, especially from Japan and Taiwan, some general grading terminology. The most commonly recognised are: Extra Choicest, Choicest, Choice, Finest, Fine, Good Medium, Medium, Good Common, Common, Nubs, Dust, and Fannings (the latter of which are used for tea bags, due to their very small size).