Compressed tea, called tea bricks, tea cakes or tea lumps, and tea nuggets according to the shape and size, are blocks of whole or finely ground black tea, green tea, or post-fermented tea leaves that have been packed in molds and pressed into block form. this was the most commonly produced and used form of tea in ancient china prior to the ming dynasty. although tea bricks are less commonly produced in modern times, many post-fermented teas, such as pu-erh, are still commonly found in bricks, discs, and other pressed forms. tea bricks can be made into beverages like tea or eaten as food, and were also used in the past as a form of currency.

Source: Wikipedia