The term means what has a form or what has a formal substance. It generally indicates existing and concrete things. The term “what is under form” comes from The Book of Changes. It is used as the opposite of “what is above form.”“Form” indicates physical shape. “What is under form” refers to the state after a physical shape has emerged, namely, physical existence. That which has a form is called “an object.” What is under form takes what is above form as the basis of its existence.

What is above form is called “Dao,” and what is under form is called “an object.” (The Book of Changes)