Amended: What Emptiness Really Means in Buddhism
"Emptiness" is one of the most often misunderstood, yet most important teachings in Buddhism - because the full realisation of this truth leads to nothing less than liberation in Enlightenment. Misunderstanding it, however, results in delusion, the opposite of Enlightenment. Realising the true nature of Emptiness is thus crucial for all Buddhists - it is the core of the wisdom of Buddhadharma (the Buddha's teachings on phenomena that leads to Enlightenment, ie. True Happiness.)
Emptiness does NOT refer to physical emptiness such as open space. Emptiness is NOT physical nothingness. Emptiness refers to first and third aspects of the Three Universal Characteristics [Anicca, Dukkha (dissatisfaction due to not realising Anicca and Anatta) and Anatta], which describe everything in the universe - both the mental (of mind) and material (of matter). Emptiness combines the reality of Anicca (the truth of the constant changing of all mind and matter from moment to moment) and Anatta (the truth of the lack of fixed, lasting self-nature or substantiality, in all mind and matter due to Anicca).
In short, Emptiness means everything (all phenomena) is "empty" of any substantiality due to constant change. As taught clearly in the Heart Sutra, "...the Five Aggregates (composites of the universe - mind and matter) are all empty.... Form is Emptiness. Emptiness is Form..." "Form" here refers to physical phenomena that is constantly fluxing. This fluxing also applies to the other four mental aggregates of feeling, perception, mental formations and consciousness. Thus, "forms" are still here, though changing all the time. In other words, forms are always "forming" or "unforming" - always transforming. This clearly does NOT mean there is nothing; just that there is nothing substantial. When we realise this, we will function in this world without delusion (but with wisdom), and with no attachment and aversion (but with generosity and compassion) with respect to any phenomenon. This itself is the state of Enlightenment.
An example of Emptiness at play is how clouds come and go. Clouds, which have form, are actually changing all the time (shape-shifting, changing state by becoming rain...), and are thus unsubstantial, lacking in fixed nature. All other material and mental phenomena (eg. thoughts) are likewise when perceived clearly enough - including "you" and "me." Knowing and seeing this in totality, and we become free as freedom can be. -Shen Shi'an (www.moonpointer.com) pic:mtholyoke.edu