Chinese Formulas (groups of herbs) can be prepared and taken in a number of ways. The prescription itself is called a fāng (方 – pronounced fong). A tang is when the herbs are put in a pot and simmered for 10 minutes or up to 2 hours. A tang is the same name for soup. A pian is a tablet.
These different designations stuck onto certain formulas and became part of their full names. Over the years we tend to use them rather indiscriminately (especially among the English speakers).
But since you asked, here they are:
汤 tāng – soup of the herbs made in a pot. This process can get rather elaborate as some herbs have to cooked for a short time and others longer. All cooking should be done in a metal free jar, stone or Corning Ware. I thought this last part was silly when I began taking herbs but after I used a stone jar they really were much stronger.
散剂 sǎnjì – a powder that is simply the herbs that are ground up and usually taken right away.
丸 wán – a pill made from the herbs. Sometimes they are coated with honey (mi wan) or other pastes.
片 piàn – a tablet, sometimes coated and sometimes just the granules pressed together.
In addition there are soft extracts, syrups (like our Super Calm), lozenges and wines.