Black tea is what most of the world is familiar with and is used extensively in mass production including the ubiquitous tea-bag. The leaf is withered, rolled and oxidised, which turns it from the fresh green leaf to the familiar dark brown/black shape. Finally the tea is dried, graded and sorted.
Black tea is produced either by the CTC (cut, tear, curl/crush) or the Orthodox method. Think of CTC as a factory style process suited to mass production. The leaves are fed into large machines which shred them into small particles which can then be used for tea-bags and every-day supermarket tea. The other method is the Orthodox process which pays much more attention to the final leaf. The Orthodox process is much more wide ranging and can produce whole leaf, large pieces of leaf and much smaller broken leaves and even small dusty particles. You can tell CTC tea by their granular appearance which often look like freeze dried coffee but often much smaller dusty particles.
Black tea is known for its strong, robust flavour and is great for early morning or the post lunch pick-me-up.