In Africa, and other countries that manufacture black tea for teabags, they use the Crush, Tear and Curl (CTC) method - a further system of grading terminology. It's designed to differentiate the much smaller, grainy particles known as 'fannings'.
These extremely small pieces of tea - sometimes called 'dusts', are left over after higher quality grades of tea such as the orange pekoe are gathered and sold. Traditionally, fannings were treated as the rejects of the manufacturing process. But in the last century they've experienced a huge demand in the developing world, mainly because they are cheap and produce a very strong brew - so a little goes a long way.